Filter media with irregular structure

ABSTRACT

Articles and methods relating to filter media are generally provided. In some embodiments, a filter media has an irregular surface structure. For instance, the filter media may comprise a plurality of peaks that are irregular in one or more ways. A ratio of a peak height standard deviation to an average peak height may be greater than or equal to 0.05, and/or a ratio of a peak spacing standard deviation to an average peak spacing may be greater than or equal to 0.08. In some embodiments, a filter media comprises a non-woven fiber web having a layer thickness of greater than 0.3 mm and/or a stiffness of less than or equal to 100 mg.

FIELD

The present invention relates generally to filter media, and, moreparticularly, to filter media with an irregular structure.

BACKGROUND

Filter media can be formed of one or more fiber webs. A fiber webprovides a porous structure that permits fluid (e.g., gas, air) to flowthrough the filter media. Contaminant particles contained within thefluid may be trapped on or within the fibrous web. Filter mediacharacteristics, such as surface area and basis weight, affect filterperformance including filter efficiency, pressure drop and resistance tofluid flow through the filter. In general, higher filter efficienciesmay result in a higher resistance to fluid flow which leads to higherpressure drops for a given flow rate across the filter.

There is a need for filter media that can be used in a variety ofapplications which have a desirable balance of properties including ahigh efficiency and a low resistance to fluid flow across the filtermedia, leading to high gamma values.

SUMMARY

Filter media, related components, and related methods are generallydescribed.

In some embodiments, a filter media is provided. The filter mediacomprises a non-woven fiber web having a stiffness of less than or equalto 100 mg and an average surface height of greater than 0.3 mm.

In some embodiments, a filter media is provided. The filter mediacomprises a non-woven fiber web comprising a plurality of peaks havingan average peak height and a peak height standard deviation. A ratio ofthe peak height standard deviation to the average peak height is greaterthan or equal to 0.05. The non-woven fiber web has an average surfaceheight of greater than 0.3 mm.

In some embodiments, a filter media is provided. The filter mediacomprises a non-woven fiber web comprising a plurality of peaks havingan average peak spacing and a peak spacing standard deviation. A ratioof the peak spacing standard deviation to the average peak spacing isgreater than or equal to 0.08. The non-woven fiber web has an averagesurface height of greater than 0.3 mm.

In some embodiments, a method of fabricating a filter media is provided.The method comprises depositing a non-woven fiber web onto a reversiblystretched layer and allowing the reversibly stretched layer to at leastpartially recover. The non-woven fiber web forms a plurality of peaksduring recovery of the reversibly stretched layer.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 is a schematic depiction of a filter media in accordance withsome embodiments;

FIG. 2 is one example of a measured relative surface topography inaccordance with some embodiments;

FIG. 3 is one example of a set of line data obtained during ameasurement of relative surface topography in accordance with someembodiments;

FIG. 4 is one example of a set of line data at which the local maximahave been identified (shown as larger points), and employed to determinea peak height (Hi) and a spacing between two adjacent peaks (Di);

FIG. 5 is a schematic depiction of a filter media comprising two layersin accordance with some embodiments;

FIG. 6 is a schematic depiction of a filter media comprising threelayers in accordance with some embodiments;

FIGS. 7A-7C are a schematic depiction of a method of fabricating afilter media in accordance with some embodiments;

FIG. 8 is a schematic depiction of a filter media comprising two layersin accordance with some embodiments;

FIGS. 9A-9C are schematic depictions of a waved filter media accordingto some embodiments;

FIGS. 10-11 are photographs of an apparatus that may be used tofabricate a filter media according to some embodiments;

FIG. 12 is a plot showing gamma and percent increase in gamma as afunction of stretch according to some embodiments;

FIG. 13 is a plot showing thickness and percent increase in thickness asa function of stretch according to some embodiments;

FIG. 14 is a plot showing surface height as a function of stretchaccording to some embodiments;

FIG. 15 is a plot showing basis weight as a function of stretchaccording to some embodiments;

FIG. 16 is a plot showing gamma as a function of surface heightaccording to some embodiments;

FIG. 17 is a plot showing the ratio of peak spacing standard deviationto average peak spacing at different degrees of stretch according tosome embodiments; and

FIG. 18 is a plot showing the ratio of peak height standard deviation toaverage peak height according to some embodiments.

DETAILED DESCRIPTION

Articles and methods related to filter media are generally provided.Some embodiments relate to filter media comprising an irregularstructure. The irregular structure may be present on an external surfaceof the filter media, in the interior of the filter media, and/orthroughout the filter media. In some embodiments, the irregularstructure includes an irregular conformation (e.g., spatialconformation, surface conformation) of at least a portion of one or morelayers in the filter media. For instance, the filter media may compriseone or more layers having a surface and/or three-dimensional shape thatproduces an irregular structure. In some embodiments, the irregularstructure may be a plurality of peaks having one or more irregularcharacteristics. For instance, the plurality of peaks may have anirregular size, spacing, and/or shape. In some such cases, the pluralityof peaks may be formed by undulations in the layer and/or its surface.Advantageously, the irregular structure may serve to increase the gammaof the filter media by, e.g., increasing the relative amount of thefilter media per unit area. By way of example, a filter media comprisingcertain irregular peaks may have a larger surface area per unit area offilter media and/or a higher basis weight per unit area than certainconventional filter media. The filter media described herein may alsohave one or more desirable physical properties. For instance, the filtermedia may be relatively thin and/or have a relatively low stiffness. Insome embodiments, the filter media may have a thinness and/or stiffnessunachievable by other methods. Such lightweight, thin, and/or lowstiffness media may be desirable for a wide variety of applications,including bag filters and face masks.

Some embodiments relate to methods of forming filter media comprising anirregular structure. As will be described in further detail below, onemethod of forming such filter media comprises depositing one or morelayers onto a reversibly stretched layer and then allowing thereversibly stretched layer to at least partially recover. Duringrecovery, the reversibly stretched layer may shorten along the directionin which it was stretched, possibly to its pre-stretched dimension. Therecovering reversibly stretched layer may pull any layer(s) depositedthereon with it as it recovers. The recovery process may cause thefilter media, and/or one or more portions thereof, to comprise anirregular structure, such as a plurality peaks having one or moreirregular characteristics. Without wishing to be bound by any particulartheory, it is believed that forming peaks in this manner may beparticularly facile, and/or may cause peaks with a particularlydesirable irregular morphology to form. However, it should also beunderstood that other methods of forming the structures described hereinare also possible.

One non-limiting example of a filter media comprising an irregularstructure is shown in FIG. 1. In FIG. 1, the irregular structure ispresent at least at the surface of the filter media; therefore, FIG. 1shows a filter media comprising an irregular structure at the surface.The filter media 1000 shown in FIG. 1 comprises a plurality of peaks100. The plurality of peaks 100 comprises peaks 10, 20, 30, 40, and 50separated by troughs 60, 70, 80, and 90. Each peak has a height and awidth. The peaks not on the outer edges of the filter media (i.e., peaks20, 30, and 40) have two nearest neighbor spacings; those on the outeredges of the filter media (i.e., peaks 10 and 50) have one nearestneighbor spacing. By way of example, the peak 40 has a height 40H, awidth 40W, and two nearest neighbor spacings 40A and 40B. These featuresof the peaks may be determined with the aid of a scanning opticalmicroscope, such as a Keyence VR-3000G2, Measurement Unit Model VR3200Wide-Area 3D Measurement system. The scanning optical microscope may beemployed to measure the surface topography of the filter media accordingto the standard described in ISO 25178 (2006) at a resolution in each ofthe x- and y-axes of at least 25 microns and in the z-axis of at least0.5 microns. This measurement yields a matrix of numerical valuesrepresenting the measured surface height at a set of points on thesample, where the x- and y-positions of each measured surface height aregiven by the column and row, respectively, of the matrix. Then, a valueof z of which 95% of the points making up the measured surfacetopography are above and 5% of the points making up the measured surfacetopography are below may be defined as a reference height (shown asdashed line 2 in FIG. 1). This reference height may be subtracted fromthe height of each point in the measured surface topography to yield arelative height of each point in the measured surface topography and arelative surface topography made up of the relative height values.

The relative surface topography may then undergo further computationalprocessing according to ISO 16610-21:2011 to determine the height ofeach peak. The computational process may include the following sequenceof steps: (1) removal of the outer 10% of points from each edge toreduce edge effects; (2) application of a Gaussian filter with a kernelsize of 30 pixels to smooth the resultant data; (3) conversion of theresultant data into a set of line data by selecting the 40^(th) row; and(4) identification of the local maxima. The local maxima identified instep (4) are the peak heights. The spacing between two peaks may bedetermined by finding the difference between the positions of the pointsat which these local maxima occur. FIG. 2 shows one example of arelative surface topography measured according to this procedure afterstep (2), and FIG. 3 shows one example of a set of line data measuredaccording to this procedure after step (3). FIG. 4 shows one example ofa set of line data at which the local maxima have been identified (shownas larger points), and employed to determine a peak height (Hi) and aspacing between two adjacent peaks (Di).

In some embodiments, like that shown in FIGS. 1-4, the peaks within theplurality of peaks may differ from each other in one or more ways. Forinstance, a plurality of peaks may comprise two or more peaks havingdiffering heights, differing spacings from their nearest neighbor(s),and/or differing shapes. By way of example, with reference to FIG. 1,the height 40H of the peak 40 is different than the height 20H of thepeak 20. As another example, the spacing 40A between the peaks 30 and 40is different than the spacing 40B between the peaks 40 and 50. In someembodiments, a plurality of peaks comprises no two peaks that have thesame height, no two sets of peaks that have the same spacing, and/or notwo peaks that have the same width. For instance, the irregularstructure and/or the filter media may not comprise a peak having thesame height, spacing, and/or width as another peak.

In some embodiments, a plurality of peaks comprises two or more peaksthat are similar in one or more ways. For instance, a plurality of peaksmay comprise two peaks having the same height, two sets of peaks havingthe same spacing, and/or two peaks having the same width. By way ofexample, with reference to FIG. 1, the height 20H of the peak 20 has thesame value as the height 50H of the peak 50. In some embodiments, aplurality of peaks comprises two or more peaks that are similar in oneor more ways (e.g., that have the same height, same spacing to a nearestneighbor, and/or same width) and two or more peaks that are different inone or more ways (e.g., that have differing heights, differing spacingsfrom their nearest neighbors, and/or differing widths). With referenceagain to FIG. 1, the plurality of peaks 100 comprises peaks 20 and 50having heights 20H and 50H with the same value, and also comprises apeak 40 with a height 40H having a different value than 20H and 50H.

It should be understood that an irregular structure may be present atany location within the filter media, but need not be present at alllocations. For instance, some filter media may, like the filter mediashown in FIG. 1, comprise a first surface that has an irregularstructure (e.g., plurality of peaks) and comprise a second surfaceopposite the first surface that is relatively regular (e.g., flat) incomparison or lacks an irregular structure (e.g., peaks) entirely. Somefilter media may, unlike the filter media shown in FIG. 1, include twoopposing surfaces, each of which comprises an irregular structure. Forinstance, some filter media may comprise two opposing surfaces, each ofwhich comprises a plurality of peaks and/or each of which comprises aplurality of peaks that is irregular in one or more ways. In someembodiments, as will be described in more detail below, a filter mediacomprises a first surface comprising a first plurality of peaksirregular in one or more ways, and a second surface that comprises asecond plurality of peaks similar to a plurality of troughs positionedbetween the peaks in the first plurality of peaks in all ways except foramplitude. The second plurality of peaks may have the same (orsubstantially similar) position, shape, spacing, and/or width of theplurality of troughs positioned between the peaks in the first pluralityof peaks, but may have smaller heights.

Filter media described herein should be understood to comprise anirregular structure if one or more portions thereof (e.g., one or morelayers therein, one or more surfaces thereof) comprises an irregularstructure. The irregular structure (e.g., plurality of peaks) may belocated at one or more surfaces of the filter media, in the interior ofthe filter media, and/or throughout the filter media. By way of example,a filter media comprising an irregular structure may comprise: aplurality of peaks irregular in one or more ways that is present at oneor more surfaces of the filter media; a plurality of peaks that extendsthrough one or more layers of the filter media; and/or a plurality ofpeaks that is present at one or more surfaces of a layer of the filtermedia.

It should also be understood that in embodiments in which the irregularstructure is not present at an exterior surface of the filter media, thecharacteristics of the irregular structure may be measured by removingthe portions of the filter media that obstruct the irregular structurefrom measurement and measuring the irregular structure as describedabove. For instance, in some embodiments, a filter media includes twoopposing layers that lack an irregular structure, but comprises a layerpositioned between the two opposing layers lacking an irregularstructure that comprises an irregular structure (e.g., plurality ofpeaks irregular in one or more ways). For such filter media, a layercomprising one of the surfaces lacking the irregular structure may beremoved so that the irregular structure is exposed, and features ofinterest of the exposed irregular structure may be measured by opticalmicroscopy as described above.

In some embodiments, a filter media comprises one or more layers. Forinstance, by way of reference to FIG. 1, a filter media 1000 may be asingle layer filter media. As another example, also by way of referenceto FIG. 1, filter media 1000 may be a filter media comprising two ormore layers. FIG. 5 shows one non-limiting embodiment of a filter media1001 comprising a first layer 201 and a second layer 301. In someembodiments, the filter media may comprise one or more layers comprisingan irregular structure. The irregular structure may include an irregularspatial conformation of the layer. For instance, a layer, or portionthereof, may have a non-planar spatial conformation that has one or moreirregular characteristics. In some embodiments, the full thickness ofthe layer, or the full thickness of a portion thereof, may be arrangedinto three-dimensional peaks and troughs. In such cases, eachnon-terminal peak is adjacent to a trough and each non-terminal troughis adjacent to a peak. In other words, a layer may have a structure suchthat each peak on a first side of the layer has a corresponding troughon the opposite side of the layer and each trough on the first side ofthe layer has a corresponding peak on the opposite side of the layer. Aplurality of troughs may be similar in one or more ways to a pluralityof peaks to which it corresponds and/or a plurality of peaks may besimilar in one or more ways to a plurality of troughs to which itcorresponds. For instance, a corresponding pair of troughs and peaks maybe positioned in substantially the same location, may have substantiallythe same peak height, may have substantially the same peak width, mayhave substantially the same peak shape, and/or may have substantiallythe same nearest neighbor spacing(s). A layer that that is arranged suchthat its full thickness is arranged into three-dimensional peaks andtroughs may be referred to as a layer comprising a plurality of peaksthat extends through the full thickness of the layer and/or as anundulated layer.

One example of an undulated layer is the layer 201 in FIG. 5. The layer201 in FIG. 5 comprises a plurality of peaks 101 comprising peaks 11,21, 31, 41, and 51 separated by troughs 61, 71, 81, and 91. The troughs61, 71, 81, and 91 together form a plurality of troughs 101T (notshown). These peaks and troughs are present at the upper side of thelayer 201 (and of the filter media 301). The plurality of peaks 101 hasa corresponding plurality of troughs 101O (not shown) comprising troughs11O, 21O, 31O, 41O, and 51O on the bottom side of the layer 201 and theplurality of troughs 101T (not shown) has a corresponding plurality ofpeaks 101TO (not shown) comprising peaks 61O, 71O, 81O, and 91O. In someembodiments, when viewed in cross-section, the outline of the topsurface of an undulated layer (e.g., layer 201) may be substantially thesame as the outline of the bottom surface of the undulated layer.

In some embodiments, an undulated layer has a structure indicative of alayer that was not undulated at some point in time and that underwent aprocess in which it was undulated. Layers that are undulated maycomprise portions that are in tension (e.g., upper surfaces of peaks,lower surfaces of troughs positioned between peaks) and/or portions thatare in compression (e.g., lower surfaces of peaks, upper surfaces oftroughs positioned between peaks). Layers may be undulated by a varietyof suitable processes, such as folding, crinkling, gathering, and thelike. In some embodiments, thermal shrinkage may be performed toundulate one or more layers. For instance, one or more layers may bedisposed on a layer with high thermal shrinkage, and the layer with highthermal shrinkage may be heated, causing it to shrink and causing theone or more layers disposed thereon to become undulated.

In some embodiments, a filter media comprises a layer that does notinclude an irregular structure. The layer not including the irregularstructure may not include any peaks (e.g., it may be relatively flat),or it may include a plurality of peaks that is regular. For instance,like that shown in FIG. 5, a filter media may comprise one layerincluding an irregular structure (e.g.

plurality of peaks) and one layer that does not include an irregularstructure (e.g., peaks). For example, filter media 1001 shown in FIG. 5comprises a layer 201 that includes a plurality of peaks (e.g., 11, 21,31, 41, and 51) and also comprises a layer 301 that does not include anypeaks. In embodiments in which a layer, such as a layer 201, includes aplurality of peaks, the peaks may have one or more irregularcharacteristics as described herein. In some embodiments, a filter mediacomprises two or more layers comprising an irregular structure (e.g.,two or more layers comprising pluralities of peaks irregular in one ormore ways) and two or more layers that do not include an irregularstructure (e.g., two or more layers lacking peaks or comprising aplurality of peaks with a regular structure). For such embodiments, thelayers may be arranged with respect to each other in a variety ofsuitable manners. For example, two layers that each comprise a pluralityof peaks irregular in one or more ways are positioned on opposite sidesof a layer that lacks a plurality of peaks irregular in one or moreways. A filter media with this structure may be fabricated by gatheringtwo layers on opposite sides of a reversibly stretchable layer. Asanother example, two layers that each lack a plurality of peaksirregular in one or more ways may be positioned on opposite sides of alayer comprising a plurality of peaks irregular in one or more ways. Forinstance, one or more layers comprising a plurality of peaks may bepositioned between two outer layers that lack peaks entirely and/or arerelatively flat. In some embodiments, a filter media exclusivelycomprises layers comprising pluralities of peaks irregular in one ormore ways.

Some filter media, like that shown in FIG. 5, include a single layerthat comprises a plurality of peaks. Some filter media include two ormore layers that each comprise a plurality of peaks. FIG. 6 shows onenon-limiting embodiment of a filter media comprising two layers thateach comprise pluralities of peaks. In FIG. 6, a filter media 1003comprises a first layer 203, a second layer 303, and a third layer 403.The first layer 203 and the third layer 403 each comprise two opposingsurfaces. In both the first layer 203 and the third layer 403, the firstsurface comprises a plurality of peaks separated by a plurality oftroughs. The surface opposing the first surface in each of these layerscomprises a plurality of troughs corresponding to the peaks present inthe first surface of the layer and a plurality of peaks corresponding tothe troughs present in the first surface of the layer.

In some embodiments, a filter media comprises two or more layers thatare undulated together. For instance, in FIG. 6, the first layer and thethird layer are also both undulated layers that are undulated together.In other words, both the first layer and the third layer are undulated,and the first layer comprises a first plurality of peaks that issubstantially similar to a second plurality of peaks present in thethird layer. With reference to FIG. 6, the plurality of peaks present inthe upper surface of the layer 203 is substantially similar to theplurality of peaks present in the upper surface of the layer 403. Insome cases in which a first layer and a third layer are undulatedtogether, the plurality of peaks and troughs in the first layer issubstantially the same as the third layer. In some embodiments, a filtermedia comprises two or more layers that are undulated, but which are notundulated together. For instance, a filter media may comprise two layersthat are undulated on opposite sides of a layer that is not undulated.As another example, a filter media may comprise a first layer and asecond layer that are both undulated and comprise undulationssubstantially similar in position, but for which the undulations have asubstantially different amplitude (e.g., substantially different averagepeak heights). Some filter media may comprise some layers that areundulated together and some layers that are undulated separately.

A variety of suitable types of layers may be included in the filtermedia described herein, such as efficiency layers, scrims, nanofiberlayers, carrier layers, and support layers. Some filter media include atmost one of any type of layer (e.g., a filter media including one scrimand one efficiency layer; a filter media including one scrim, oneefficiency layer, and one nanofiber layer; a filter media including onescrim, one efficiency layer, one nanofiber layer, and one carrierlayer). Some filter media include two or more layers of a single kind(e.g., a filter media comprising one scrim and two efficiency layers; afilter media comprising one scrim, two efficiency layers, and onenanofiber layer). It should be understood that references to a firstlayer, a second layer, a third layer, and the like may refer to any typeof layer and that the layers described herein may be combined with eachother in a variety of different combinations and in a variety ofdifferent orders. It should also be understood that references to anon-woven fiber web may refer to any type of non-woven fiber web layer,such as an efficiency layer that is a non-woven fiber web, a nanofiberlayer that is a non-woven fiber web, a scrim that is a non-woven fiberweb, a carrier layer that is a non-woven fiber web, and/or a supportlayer that is a non-woven fiber web. The properties of different typesof layers that may be included in the filter media are described infurther detail below.

The filter media described herein may be manufactured in a variety ofsuitable manners. One method of manufacturing filter media that may beparticularly advantageous is shown in FIGS. 7A-7C. In this method, alayer with relatively low stiffness is gathered to form a layer that isundulated using a layer capable of undergoing a reversible stretch. Thelayer capable of undergoing a reversible stretch is stretched, and thelayer with the relatively low stiffness is deposited onto the layercapable of undergoing a reversible stretch when in the stretched state(i.e., when it is in the form of a reversibly stretched layer). Then,when the reversibly stretched layer recovers, it pulls the layer withthe relatively low stiffness back with it, gathering the layer with therelatively low stiffness. The reversibly stretched layer may recoverfully (i.e., to its initial dimensions prior to being stretched) orpartially (i.e., to dimensions between its initial dimensions prior tobeing stretched and its dimensions when in the stretched state). Inother words, a layer capable of undergoing a reversible stretch may bestretched in a manner that is entirely reversible or in a manner that ispartially reversible and partially irreversible. FIG. 7A shows apossible first step of reversibly stretching a layer capable ofundergoing a reversible stretch, such as a scrim, to a stretched state.FIG. 7B shows a possible second step of depositing a layer, such as anefficiency layer, onto the reversibly stretched layer. FIG. 7C shows therecovery of the reversibly stretched layer. During the recovery process,the layer with the relatively low stiffness gathers and forms aplurality of peaks that are irregular in height, spacing, width, and/orshape.

In general, any suitable number of layers may be undulated (e.g., bygathering) using a layer capable of undergoing a reversible stretch. Insome embodiments, not shown in FIGS. 7A-7C, one or more further layersmay be deposited onto the reversibly stretched layer after deposition ofa layer with relatively low stiffness thereon. In some embodiments, oneor more further layers may be deposited onto the reversibly stretchedlayer together with a layer having a relatively low stiffness. Thefurther layer or layers may be deposited prior to recovery of thereversibly stretched layer. For instance, a second efficiency layer maybe deposited onto a first efficiency layer deposited on a reversiblystretched scrim, a nanofiber layer may be deposited onto an efficiencylayer deposited on a reversibly stretched scrim, or two efficiencylayers may be deposited together onto a reversibly stretched scrim.Then, as shown in FIG. 7C, the reversibly stretched layer may be allowedto recover. Layers deposited on the reversibly stretched layer (e.g., onthe layer with the relatively low stiffness and/or together with thelayer with the relatively low stiffness) may become undulated (e.g., bygathering) during this step. In some embodiments, like the embodimentshown in FIG. 6, the layers may undulated and/or gathered together. Thefurther layer or layers deposited onto the reversibly stretched layer inaddition to the layer with the relatively low stiffness may also have arelatively low stiffness, which may promote this advantageous gathering.In some embodiments, one or more further layers may be deposited ontothe reversibly stretched layer after recovery of the reversiblystretched layer.

In some embodiments, like the embodiment shown in FIGS. 7A-7C, a layerto be gathered is deposited directly onto a reversibly stretched layerand the resultant gathered layer and recovered layer are directlyadjacent. As used herein, when a layer is referred to as being “on” or“adjacent” another layer, it can be directly on or adjacent the layer,or an intervening layer or material also may be present. A layer that is“directly on”, “directly adjacent” or “in contact with” another layermeans that no intervening layer or material is present.

In some embodiments, a layer to be gathered is deposited onto a layer ormaterial deposited onto the reversibly stretched layer, and theresultant gathered layer and recovered layer are adjacent but notdirectly adjacent. For example, a layer to be gathered may be depositedon an adhesive deposited on the reversibly stretched layer, such thatthe adhesive is positioned between the resultant gathered layer andrecovered layer. In some embodiments in which an adhesive is positionedbetween the layer to be gathered and the reversibly stretched layer, theadhesive may be deposited onto the reversibly stretched layer prior tostretching and/or after stretching. For example, an adhesive may bedeposited onto a scrim, the scrim may be stretched, and then anefficiency layer may be deposited onto the stretched scrim. In thiscase, the adhesive is stretched along with the scrim along the directionthat the scrim is stretched. The efficiency layer may bond less well tothe scrim along the direction the scrim is stretched, and so may detachfrom the scrim at certain positions along the opposite direction whenthe scrim is allowed to recover. In such cases, the efficiency layer maybe gathered, and the scrim may comprise undulations (or be undulated)that follow the undulations in the efficiency layer. The undulations inthe scrim may be much smaller than those in the efficiency layer (i.e.,they may have a much smaller average peak height), and so the scrim maybe considered to be relatively, but not perfectly, flat in comparison tothe efficiency layer.

When a reversibly stretched layer is stretched, the direction of stretchmay generally be selected as desired. In some embodiments, a reversiblystretched layer may be stretched in a machine direction. In someembodiments, a reversibly stretched layer may be stretched in a crossdirection. When stretched, the reversibly stretched layer may bestretched to a variety of suitable lengths. The reversibly stretchedlayer may be stretched to a length of greater than or equal to 50%,greater than or equal to 75%, greater than or equal to 100%, greaterthan or equal to 125%, greater than or equal to 150%, greater than orequal to 175%, greater than or equal to 200%, greater than or equal to225%, greater than or equal to 250%, greater than or equal to 275%,greater than or equal to 300%, greater than or equal to 325%, greaterthan or equal to 350%, greater than or equal to 375%, greater than orequal to 400%, greater than or equal to 450%, greater than or equal to500%, greater than or equal to 600%, or greater than or equal to 800% ofits initial length. In some embodiments, the reversibly stretched layeris stretched to a length of less than or equal to 1000%, less than orequal to 800%, less than or equal to 600%, less than or equal to 500%,less than or equal to 450%, less than or equal to 400%, less than orequal to 375%, less than or equal to 350%, less than or equal to 325%,less than or equal to 300%, less than or equal to 275%, less than orequal to 250%, less than or equal to 225%, less than or equal to 200%,less than or equal to 175%, less than or equal to 150%, less than orequal to 125%, less than or equal to 100%, or less than or equal to 75%of its initial length. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 50% and less than or equalto 1000%, greater than or equal to 100% and less than or equal to 400%,or greater than or equal to 200% and less than or equal to 300%). Otherranges are also possible.

Layer(s) deposited on a reversibly stretched layer in a reversiblystretched state may recover with the reversibly stretched layer to arecovered length, undergoing a reduction in length. The reduction inlength may be equivalent to the corresponding reduction in lengthexperienced by the reversibly stretched layer upon recovery. When thereversibly stretched layer exhibits substantially complete recovery, thereduction in length of the layer(s) may fall within one or more rangesthat may be derived from the ranges above by the following formula:Percent reduction in length=(1-100/(100+percent stretch))*100%.

For instance, a layer deposited on a reversibly stretched layerstretched to 50% of its initial length that fully recovers would have acorresponding reduction in length of 33% of its initial length. Asanother example, a layer deposited on a reversibly stretched layerstretched to 1000% of its initial length that fully recovers would havea corresponding reduction in length of 91% of its initial length.

In some embodiments, a filter media comprising an irregular structuremay further comprise one or more additional structures. The additionalstructure may include peaks, troughs, undulations, and/or otherfeatures. The additional structure or structures may be regular (e.g., aplurality of regular peaks) or irregular (e.g., a plurality of peaksirregular in one or more ways). In general, the additional structure,whether regular or irregular, may be on a different length scale thanthe irregular structure. For instance, an additional structure maycomprise one or more features (e.g., peaks, troughs) with a size greaterin magnitude than a feature (e.g., a peak, a trough) of the irregularstructure. A non-limiting example of a filter media including anirregular structure and an additional structure is shown in FIG. 8. Asillustrated in FIG. 8, a filter media 1005 may include both an irregularstructure and an additional structure 500. The irregular structure maybe present on an external surface of the filter media, in the interiorof the filter media, and/or throughout the filter media. In someinstances, as illustrated in FIG. 8, the irregular structure may bepresent on an external surface of the filter media and/or extend throughthe full thickness of one or more layers of the filter media. In somecases, an undulated layer in the filter media, such as the undulatedlayer 305 in FIG. 8, may comprise an irregular structure as describedherein. As for the irregular structure, the presence of an additionalstructure comprising regular and/or irregular undulations (e.g., aplurality of peaks) may increase the relative amount of the filter mediaper unit area, which may desirably increase the gamma of the filtermedia.

In some embodiments, one or more layers in a filter media may compriseboth an irregular structure and an additional structure. By way ofexample, in some embodiments, a filter media comprises a layercomprising a plurality of peaks irregular in one or more ways andcomprising an additional structure. The plurality of peaks irregular inone or more ways typically, but not always, has a length scale smallerthan the additional structure. In some embodiments, one or more layersin a filter media are undulated on two length scales. For instance, alayer in a filter media may be undulated in an irregular manner and thenfurther undulated on a larger length scale to form the additionalstructure. The plurality of peaks making up the irregular undulationsmay, at least partially, have a different orientation than theundulations forming the additional structure and/or a different averagepeak height than the undulations forming the additional structure.

In some embodiments, the additional structure or structures are formedby an additional step (e.g., pleating, waving) that imparts theadditional structure to the filter media. For instance, a filter mediacomprising an irregular structure including a plurality of peaks may bepleated to impart regular peaks to the filter media. The peak heights,peak spacing, and/or peak size of the pleats may be significantly largerthan the same features of the irregular structure. In some such cases,the pleating may serve to impart a relatively macroscale structure tothe filter media as a whole while the irregular structure imparts arelatively microscale structure to the filter media. In someembodiments, the additional structure may be relatively macroscale incomparison to the irregular structure and may be formed by subjecting afilter media, such as filter media 1001 in FIG. 1, to a process thatforms undulations, such as pleating and/or waving, to form a filtermedia including an irregular structure and an additional structure, suchas filter media 1005.

A variety of techniques may be employed to form an additional structurein a layer comprising an irregular structure. Some such techniquescomprise undulating a layer comprising a first plurality of peaks makingup the irregular structure, such as a layer comprising a plurality ofpeaks irregular in one or more ways, to form a second plurality of peaksmaking up the additional structure. By way of example, the layercomprising the first plurality of peaks, and any other layers undulatedtogether with the layer comprising the plurality of peaks, may bepleated and/or waved. Pleating, and/or waving the layer(s) may result inthe formation of a second plurality of peaks that is relatively regular.As another example, the layer comprising the first plurality of peaks,and any other layers undulated together with the layer comprising theplurality of peaks, may undergo one or more of the processes describedabove to form a second plurality of peaks irregular in one or more ways.In other words, the additional structure may be an irregular structureand/or may be formed by one of the methods employed to form the firstplurality of peaks. For instance, the layer comprising the firstplurality of peaks, and any other layers undulated together with thelayer comprising the first plurality of peaks, may be folded, crinkled,gathered, and/or disposed on a layer that undergoes thermal shrinkage.

In some embodiments, a filter media comprising one or more layerscomprising an undulated layer further comprises one or more additionalsupport layers (e.g., one or more fibrous support layers) that hold theone or more undulated layers in the undulated configuration. The supportlayer(s) may lack a plurality of irregular peaks and/or may berelatively flat prior to undulation. FIG. 9A illustrates one exemplaryembodiment of a filter media in which a layer is undulated by waving andheld in the waved configuration by two support layers. FIG. 9A depicts afilter media 1006 having at least one waved layer and at least onesupport layer that holds the waved layer in a waved configuration tomaintain separation of peaks and troughs of adjacent waves of the wavedlayer. In the illustrated embodiment, the filter media 1006 includes anefficiency layer 12, a first, downstream support layer 14, and a second,upstream support layer 16 disposed on opposite sides of the efficiencylayer 12. Although not shown, the efficiency layer 12 may comprise anirregular structure, such as a plurality of peaks irregular in one ormore ways. The first and second support layers 14 and 16 may lack aplurality of peaks prior to waving with the efficiency layer 12. Thesupport layers 14, 16 can help maintain the efficiency layer 12, andoptionally any additional layers described elsewhere herein, in thewaved configuration. The additional layers may have one or morestructural features described elsewhere herein with respect to the layercomprising the plurality of peaks irregular in one or more ways. Forinstance, each additional layer may or may not, independently: comprisea plurality of peaks, be an undulated layer prior to waving, be agathered layer prior to waving, be undulated with one or more otherlayers, and/or be gathered with one or more other layers.

With further reference to FIG. 9A, in some embodiments, a scrim ispositioned between the support layer 14 and the efficiency layer 12and/or between the support layer 16 and the efficiency layer 12. In someembodiments a nanofiber layer is positioned between the support layer 14and the efficiency layer 12 and/or between the support layer 16 and theefficiency layer 12. While two support layers 14, 16 are shown, thefilter media 10 need not include both support layers. Where only onesupport layer is provided, the support layer can be disposed upstream ordownstream of the filtration layer(s).

The filter media 1006 can also optionally include one or more outer orcover layers located on the upstream-most and/or downstream-most sidesof the filter media 1006. FIG. 9A illustrates a top layer 18 disposed onthe upstream side of the filter media 1006 to function, for example, asan upstream dust holding layer. The top layer 18 can also function as anaesthetic layer. The layers in the illustrated embodiment are arrangedso that the top layer 18 is disposed on the air entering side, labeledI, the second support layer 16 is just downstream of the top layer 18,the efficiency layer 12 is disposed just downstream of the secondsupport layer 16, and the first support layer 14 is disposed downstreamof the efficiency layer 12 on the air outflow side, labeled O. Thedirection of air flow, i.e., from air entering I to air outflow O, isindicated by the arrows marked with reference A.

The outer or cover layer can alternatively or additionally be a bottomlayer disposed on the downstream side of the filter media 1006 tofunction as a strengthening component that provides structural integrityto the filter media 1006 to help maintain the waved configuration. Theouter or cover layer(s) can also function to offer abrasion resistance.FIG. 9B illustrates another embodiment of a filter media 1006B that issimilar to filter media 1006 of FIG. 9A. In this embodiment, the filtermedia 1006B does not include a top layer, but rather has an efficiencylayer 12B, a first support layer 14B disposed just downstream of theefficiency layer 12B, a second support layer 16B disposed just upstreamof the efficiency layer 12B on the air entering side I, and a bottomlayer 18B disposed just downstream of the first support layer 14B on theair exiting side O. Further layers may be positioned between theefficiency layer and the support layers shown in FIG. 9B, such as scrimlayer(s) and/or nanofiber layer(s). Furthermore, as shown in theexemplary embodiments of FIGS. 9A and 9B, the outer or cover layer(s)can have a topography different from the topographies of the efficiencylayer and/or any support layers. For example, in either a pleated ornon-pleated configuration, the outer or cover layer(s) may be non-waved(e.g., substantially planar, lacking undulations, and/or lacking aplurality of peaks irregular in one or more ways), whereas theefficiency layer, any support layers, and/or any layer(s) positionedbetween the efficiency layer and the support layer(s) may have a wavedconfiguration. A person skilled in the art will appreciate that avariety of other configurations are possible, and that the filter mediacan include any number of layers in various arrangements.

It should be understood that while some embodiments relate to wavedfilter media, like those shown in FIGS. 9A and 9B, some filter mediathat are not waved may have one or more of the features shown in FIGS.9A and/or 9B. By way of example, a layer comprising a first plurality ofpeaks, such as a layer comprising a plurality of peaks irregular in oneor more ways, may be further undulated to form a second plurality ofpeaks by a method other than waving and may be positioned in a filtermedia comprising one or more support layers and/or one or more outer orcover layers. The method other than waving may be any of those describedherein, such as pleating, folding, crinkling, gathering, and/or thermalshrinking.

Filter media comprising an irregular structure and an additionalstructure, such as filter media comprising one or more layers, may bemanufactured in a variety of suitable manners. In an exemplaryembodiment the layer(s) are waved (e.g., layer(s) comprising a pluralityof peaks irregular in one or more ways, efficiency layer(s), scrim(s),nanofiber layer(s), and/or support layer(s)). The layer(s) to be wavedmay be positioned adjacent to one another in a desired arrangement fromair entering side to air outflow side, and the combined layers may beconveyed between first and second moving surfaces that are traveling atdifferent speeds, such as with the second surface traveling at a speedthat is slower than the speed of the first surface. A suction force,such as a vacuum force, can be used to pull the layers toward the firstmoving surface, and then toward the second moving surface as the layerstravel from the first to the second moving surfaces. The speeddifference may cause the layers to form z-direction waves as they passonto the second moving surface, thus forming peaks and troughs in thelayers. The speed of each surface can be altered to obtain the desirednumber of waves per inch. The distance between the surfaces can also bealtered to determine the amplitude of the peaks and troughs, and in anexemplary embodiment the distance is adjusted between 0.025 inches to 4inches. For example, the amplitude of the peaks and waves may be between0.1 inch and 4.0 inches, e.g., between 0.1 inch and 1.0 inch, between0.1 inch and 2.0 inches, or between 3.0 inches and 4.0 inches. Forcertain applications, the amplitude of the peaks and waves may bebetween 0.1 inch and 1.0 inch, between 0.1 inch and 0.5 inches, orbetween 0.1 inch and 0.3 inches. The properties of the different layerscan also be altered to obtain a desired filter media configuration. Inan exemplary embodiment the filter media has 2 to 6 waves per inch, witha height (overall thickness) in the range of between 0.025 inches and 2inches, however this can vary significantly depending on the intendedapplication. For instance, in other embodiments, the filter media mayhave 2 to 4 waves per inch, e.g., 3 waves per inch. The overallthickness of the media may be between 0.025 inches and 4.0 inches, e.g.,between 0.1 inch and 1.0 inch, between 0.1 inch and 2.0 inches, orbetween 3.0 inches and 4.0 inches. For certain applications, the overallthickness of the media may be between 0.1 inch and 0.5 inches, orbetween 0.1 inch and 0.3 inches. As shown in FIG. 9A, in someembodiments, a single wave W extends from the middle of one peak to themiddle of an adjacent peak. Thickness of the waved filter media can bedetermined according to the Edana WSP 120.1 Standard (2005) with apressure foot selected to have a 2 ounce load and a 1 square inch area.

In the embodiment shown in FIG. 9A, when the efficiency layer 12 and thesupport layers 14, 16 are waved, the resulting efficiency layer 12 willhave a plurality of peaks P and troughs T on each surface thereof (i.e.,air entering side I and air outflow side O), as shown in FIG. 9C. Thesupport layers 14, 16 will extend across the peaks P and into thetroughs T so that the support layers 14, 16 also have wavedconfigurations. A person skilled in the art will appreciate that a peakP on the air entering side I of the efficiency layer 12 will have acorresponding trough T on the air outflow side O. Thus, the downstreamsupport layer 14 will extend into a trough T, and exactly opposite thatsame trough T is a peak P, across which the upstream support layer 16will extend. Since the downstream support layer 14 extends into thetroughs T on the air outflow side O of the efficiency layer 12, thedownstream coarse layer 14 will maintain adjacent peaks P on the airoutflow side O at a distance apart from one another and will maintainadjacent troughs T on the air outflow side O at a distance apart fromone another. The upstream support layer 16, if provided, can likewisemaintain adjacent peaks P on the air entering side I of the efficiencylayer 12 at a distance apart from one another and can maintain adjacenttroughs T on the air entry side I of the efficiency layer 12 at adistance apart from one another. As a result, the efficiency layer 12has a surface area that is significantly increased, as compared to asurface area of the fiber filtration layer in the planar configuration.In certain exemplary embodiments, the surface area in the wavedconfiguration is increased by at least 50%, and in some instances asmuch as 120%, as compared to the surface area of the same layer in aplanar configuration. In other words, the waved configuration maycomprise at least 50% more, or at least 120% more, of filter media areaper footprint of the filter media than an otherwise equivalent unwavedfilter media.

In embodiments in which the upstream and/or downstream support layershold the one or more other layers in a waved configuration, it may bedesirable to reduce the amount of free volume (e.g., volume that isunoccupied by any fibers) in the troughs. That is, a relatively highpercentage of the volume in the troughs may be occupied by the supportlayer(s) to give the other layer(s) structural support. For example, atleast 95% or substantially all of the available volume in the troughsmay be filled with the support layer. The support layer may have asolidity of greater than or equal to 1%, greater than or equal to 1.25%,greater than or equal to 1.5%, greater than or equal to 2%, greater thanor equal to 2.5%, greater than or equal to 3%, greater than or equal to4%, greater than or equal to 5%, greater than or equal to 7.5%, greaterthan or equal to 10%, greater than or equal to 12.5%, greater than orequal to 15%, greater than or equal to 20%, or greater than or equal to25%. The support layer may have a solidity of less than or equal to 30%,less than or equal to 25%, less than or equal to 20%, less than or equalto 15%, less than or equal to 12.5%, less than or equal to 10%, lessthan or equal to 7.5%, less than or equal to 5%, less than or equal to4%, less than or equal to 3%, less than or equal to 2.5%, less than orequal to 2%, less than or equal to 1.5%, or less than or equal to 1.25%.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 1% and less than or equal to 30%, greater thanor equal to 4% and less than or equal to 20%, or greater than or equalto 5% and less than or equal to 15%). Other ranges are also possible.

The solidity of a support layer may be determined by using the followingformula: solidity=[basis weight/(fiber density*thickness)]*100%. Thebasis weight and thickness may be determined as described elsewhereherein. The fiber density is equivalent to the average density of thematerial or material(s) forming the fiber, which is typically specifiedby the fiber manufacturer. The average density of the materials formingthe fibers may be determined by: (1) determining the total volume of allof the fibers in the filter media; and (2) dividing the total mass ofall of the fibers in the filter media by the total volume of all of thefibers in the filter media. If the mass and density of each type offiber in the filter media are known, the volume of all the fibers in thefilter media may be determined by: (1) for each type of fiber, dividingthe total mass of the type of fiber in the filter media by the densityof the type of fiber; and (2) summing the volumes of each fiber type. Ifthe mass and density of each type of fiber in the filter media are notknown, the volume of all the fibers in the filter media may bedetermined in accordance with Archimedes' principle.

Additionally, as shown in the exemplary embodiments of FIG. 9A, theextension of the support layer(s) across the peaks and into the troughsmay be such that the surface area of the support layer in contact with atop layer 18A is similar across the peaks as it is across the troughs.Similarly, the surface area of the support layer in contact with abottom layer 18B (FIG. 9B) may be similar across the peaks as it isacross the troughs. For example, the surface area of the support layerin contact with a top or bottom layer across a peak may differ from thesurface area of the support layer in contact with the top or bottomlayer across a trough by less than 70%, less than 50%, less than 30%,less than 20%, less than 10%, or less than 5%.

In certain exemplary embodiments, the downstream and/or upstream supportlayers 14, 16 can have a fiber density that is greater at the peaks thanit is in the troughs; and, in some embodiments, a fiber mass that isless at the peaks than it is in the troughs. This can result from thecoarseness of the downstream and/or upstream support layers 14, 16relative to the efficiency layer 12. In particular, as the layers arepassed from the first moving surface to the second moving surface, therelatively fine nature of the efficiency layer 12 will allow thedownstream and/or upstream support layers 14, 16 to conform around thewaves formed in the efficiency layer 12. As the support layers 14, 16extend across a peak P, the distance traveled will be less than thedistance that each layer 14, 16 travels to fill a trough. As a result,the support layers 14, 16 will compact at the peaks, thus having anincreased fiber density at the peaks as compared to the troughs, throughwhich the layers will travel to form a loop-shaped configuration.

Once the layers are formed into a waved configuration, the waved shapecan be maintained by activating binder fibers (e.g., binder fibers inone or both of the support layers) to effect bonding of the fibers. Avariety of techniques can be used to activate the binder fibers. Forexample, if bicomponent binder fibers having a core and sheath are used,the binder fibers can be activated upon the application of heat. Ifmonocomponent binder fibers are used, the binder fibers can be activatedupon the application of heat, steam and/or some other form of warmmoisture. A top layer 18 (FIG. 9A) and/or bottom layer 18B (FIG. 9B) canalso be positioned on top of the upstream support layer 16 (FIG. 9A) oron the bottom of the downstream support layer 14B (FIG. 9B),respectively, and mated, such as by bonding, to the upstream supportlayer 16 or downstream support layer 14B simultaneously or subsequently.A person skilled in the art will also appreciate that the layers canoptionally be mated to one another using various techniques other thanusing binder fibers. The layers can also be individually bonded layers,and/or they can be mated, including bonded, to one another prior tobeing waved.

The filter media described herein may be suitable for a variety offiltration applications. For instance, the filter media described hereinmay be suitable for use in HVAC bag filters, HVAC panel filters,respiratory protective equipment, medical filters, vacuum cleanerfilters, room air purifier filters, cabin air filters, and hydraulicfluid filters. Some filter media described herein may be fluid filters,such as gas filters (e.g., an filters) and/or liquid filters (e.g.,water filters, fuel filters). In some embodiments, the filter mediadescribed herein are high energy particulate air (HEPA) or ultra-lowpenetration air (ULPA) filters. These filters are required to removeparticulates at an efficiency level of greater than 99.95% and 99.9995%,respectively, per EN1822:2009. In some embodiments, the filter media mayremove particulates at an efficiency of greater than 95%, greater than99.995%, greater than 99.99995%, or up to 99.999995%. In someembodiments, the filter media may be suitable for HVAC applications.That is, the filter media may have a particulate efficiency of greaterthan or equal to about 10% and less than or equal to about 90%, orgreater than or equal to about 35% and less than or equal to about 90%.Other types of filter media and efficiencies are also possible. In someembodiments, a filter media may be a HEPA, ULPA, or HVAC filter and maybe one component of a filter element as described in more detail below.

In some embodiments, a filter media described herein may be a componentof a filter element. That is, the filter media may be incorporated intoan article suitable for use by an end user. Non-limiting examples ofsuitable filter elements include flat panel filters, V-bank filters(comprising, e.g., between 1 and 24 Vs), cartridge filters, cylindricalfilters, conical filters, and curvilinear filters. Filter elements mayhave any suitable height (e.g., between 2 inches and 124 inches for flatpanel filters, between 4 inches and 124 inches for V-bank filters,between 1 inch and 124 inches for cartridge and cylindrical filters).Filter elements may also have any suitable width (between 2 inches and124 inches for flat panel filters, between 4 inches and 124 inches forV-bank filters). Some filter elements (e.g., cartridge filters,cylindrical filters) may be characterized by a diameter instead of awidth; these filter elements may have a diameter of any suitable value(e.g., between 1 inch and 124 inches). Filter elements typicallycomprise a frame, which may be made of one or more materials such ascardboard, aluminum, steel, alloys, wood, and polymers.

The filter media described herein may perform advantageously in one ormore ways. In some embodiments, a filter media has a desirably highvalue of gamma, which is a rating applied to filter media based on therelationship between penetration and pressure drop across the media, orparticulate efficiency as a function of pressure drop across the mediaor web. Generally, higher gamma values are indicative of better filterperformance, i.e., a high particulate efficiency as a function ofpressure drop. As described above, and without wishing to be bound byany particular theory, increasing the surface area of a filter mediawill typically increase its gamma. Accordingly, the filter mediadescribed herein that have relatively high surface areas, such as filtermedia comprising an irregular structure and/or a plurality of peaksirregular in one or more ways, may also have relatively high values ofgamma. Gamma is defined by the following formula: Gamma=(−log₁₀(initialpenetration %/100)/initial pressure drop, mm H₂O)×100. Penetration,often expressed as a percentage, is defined as follows: Pen(%)=(C/C₀)*100 where C is the particle concentration after passagethrough the filter and Co is the particle concentration before passagethrough the filter. The initial penetration is the penetration measuredupon first exposure of the filter media to the particles, and theinitial pressure drop is the pressure drop measured upon first exposureof the filter media to the particles. The penetration and gammadescribed herein are those measured using NaCl particles with an averagediameter of 0.26 microns. The penetration and pressure drop can both bemeasured by employing a TSI 8130 Automated Filter Tester (8130CertiTest™ Filter Tester from TSI) with a circular opening with an areaof 100 cm² to analyze a flat-sheet filter media.

When measuring gamma, the TSI 8130 Automated Filter Tester is employedto blow an NaCl aerosol made up of NaCl particles with an averagediameter of 0.26 microns at the filter media. The NaCl particles may begenerated from a 2 wt % aqueous solution of NaCl which is caused to forman NaCl aerosol by blowing dilution air through the solution at a rateof 70 L/min at a pressure of 30 psi. The aerosol is then blown throughthe filter media at a pressure 30 psi and a rate of 32 L/min, whichcorresponds to a face velocity of 5.3 cm/s. As the TSI 8130 AutomatedFilter Tester is blowing the NaCl aerosol, both the pressure drop acrossthe filter media and the penetration of the NaCl aerosol are measured bytwo condensation nucleus particle counters simultaneously, one of whichis upstream of the filter media and one of which is downstream of thefilter media. The particle collection efficiency is reported at thebeginning of the test, and is the percentage of upstream challengeparticles collected by the filter at the beginning of the test. Theinitial pressure drop is also measured at the beginning of the test.

In some embodiments, a filter media has a gamma of greater than or equalto 8, greater than or equal to 10, greater than or equal to 15, greaterthan or equal to 20, greater than or equal to 25, greater than or equalto 30, greater than or equal to 40, greater than or equal to 50, greaterthan or equal to 75, greater than or equal to 100, greater than or equalto 125, greater than or equal to 150, greater than or equal to 175,greater than or equal to 200, greater than or equal to 225, greater thanor equal to 250, greater than or equal to 275, greater than or equal to300, greater than or equal to 330, greater than or equal to 350, orgreater than or equal to 375. In some embodiments, a filter media has agamma of less than or equal to 400, less than or equal to 375, less thanor equal to 350, less than or equal to 330, less than or equal to 300,less than or equal to 275, less than or equal to 250, less than or equalto 225, less than or equal to 200, less than or equal to 175, less thanor equal to 150, less than or equal to 125, less than or equal to 100,less than or equal to 75, less than or equal to 50, less than or equalto 40, less than or equal to 30, less than or equal to 25, less than orequal to 20, less than or equal to 15, or less than or equal to 10.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 8 and less than or equal to 400, greater thanor equal to 25 and less than or equal to 330, or greater than or equalto 30 and less than or equal to 330). Other ranges are also possible.

As described above, some filter media described herein comprise anirregular structure, which yields one or more resultant advantages. Theirregular structure may be in the form of an irregular surfacestructure. By way of example, it may take the form of a plurality ofpeaks in the surface that are irregular in one or more ways. As anotherexample, it may take the form of a plurality of peaks present at asurface of one or more layers, and/or extending through one or morelayers (e.g., in the case of undulated layers), that are irregular inone or more ways. For instance, a filter media may comprise a pluralityof peaks that is present at the surface of, and/or extends through, oneor more of the following types of layers: efficiency layers, nanofiberlayers, carrier layers, and scrims. In some embodiments, a filter mediacomprises a plurality of peaks that extends throughout the entirety ofthe filter media. In other words, a filter media may include only layersthat are undulated together and where the undulations take the form ofthe plurality of peaks irregular in one or more ways. Several featuresof pluralities of peaks irregular in one or more ways are describedbelow. It should be understood that this description may relate topluralities of peaks present at a surface of the filter media, at asurface of one or more layers therein, extending through the thicknessof the filter media, and/or extending through one or more layerstherein. These features may be features of a plurality of peaks in anundulated layer or layers and/or of a plurality of peaks that is not anundulated layer.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havean average peak height that is particularly advantageous. For instance,the plurality of peaks may have an average peak height of greater thanor equal to 0.3 mm, greater than or equal to 0.5 mm, greater than orequal to 0.75 mm, greater than or equal to 1 mm, greater than or equalto 1.5 mm, greater than or equal to 2 mm, greater than or equal to 2.5mm, greater than or equal to 3 mm, greater than or equal to 4 mm,greater than or equal to 5 mm, greater than or equal to 6 mm, greaterthan or equal to 7 mm, greater than or equal to 8 mm, or greater than orequal to 9 mm. In some embodiments, a filter media comprises a pluralityof peaks having an average peak height of less than or equal to 10 mm,less than or equal to 9 mm, less than or equal to 8 mm, less than orequal to 7 mm, less than or equal to 6 mm, less than or equal to 5 mm,less than or equal to 4 mm, less than or equal to 3 mm, less than orequal to 2.5 mm, less than or equal to 2 mm, less than or equal to 1.5mm, less than or equal to 1 mm, less than or equal to 0.75 mm, or lessthan or equal to 0.5 mm. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 0.3 mm and less than orequal to 10 mm, greater than or equal to 1 mm and less than or equal to8 mm, or greater than or equal to 3 mm and less than or equal to 7 mm).Other ranges are also possible. The average peak height may bedetermined by finding the peak height of the peaks making up theplurality of peaks by use of a scanning optical microscope, as describedabove, and then averaging these peak heights to yield an average peakheight.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havea peak height standard deviation that is particularly advantageous. Forinstance, the plurality of peaks may have a peak height standarddeviation of greater than or equal to 0.1 mm, greater than or equal to0.15 mm, greater than or equal to 0.2 mm, greater than or equal to 0.25mm, greater than or equal to 0.3 mm, greater than or equal to 0.4 mm,greater than or equal to 0.5 mm, greater than or equal to 0.75 mm,greater than or equal to 1 mm, greater than or equal to 1.25 mm, greaterthan or equal to 1.5 mm, greater than or equal to 1.75 mm, greater thanor equal to 2 mm, greater than or equal to 2.25 mm, greater than orequal to 2.5 mm, or greater than or equal to 2.75 mm. In someembodiments, a filter media comprises a plurality of peaks having a peakheight standard deviation of less than or equal to 3 mm, less than orequal to 2.75 mm, less than or equal to 2.5 mm, less than or equal to2.25 mm, less than or equal to 2 mm, less than or equal to 1.75 mm, lessthan or equal to 1.5 mm, less than or equal to 1.25 mm, less than orequal to 1 mm, less than or equal to 0.75 mm, less than or equal to 0.5mm, less than or equal to 0.4 mm, less than or equal to 0.3 mm, lessthan or equal to 0.25 mm, less than or equal to 0.2 mm, or less than orequal to 0.15 mm. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0.1 mm and less than or equalto 3 mm, greater than or equal to 0.15 mm and less than or equal to 1.5mm, or greater than or equal to 0.2 mm and less than or equal to 1 mm).Other ranges are also possible. The peak height standard deviation maybe determined by finding the peak height of the peaks making up theplurality of peaks by use of a scanning optical microscope, as describedabove, and then using standard statistical techniques to determine thestandard deviation of the peak heights to yield the peak height standarddeviation.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havea ratio of peak height standard deviation to average peak height that isparticularly advantageous. For instance, the plurality of peaks may havea ratio of peak height standard deviation to average peak height ofgreater than or equal to 0.03, greater than or equal to 0.035, greaterthan or equal to 0.04, greater than or equal to 0.045, greater than orequal to 0.05, greater than or equal to 0.055, greater than or equal to0.06, greater than or equal to 0.065, greater than or equal to 0.07,greater than or equal to 0.075, greater than or equal to 0.08, greaterthan or equal to 0.09, greater than or equal to 0.1, greater than orequal to 0.15, greater than or equal to 0.2, greater than or equal to0.25, greater than or equal to 0.3, greater than or equal to 0.35,greater than or equal to 0.4, greater than or equal to 0.45, greaterthan or equal to 0.5, greater than or equal to 0.55, greater than orequal to 0.6, greater than or equal to 0.65, greater than or equal to0.7, or greater than or equal to 0.75. In some embodiments, a filtermedia comprises a plurality of peaks having a ratio of peak heightstandard deviation to average peak height of less than or equal to 0.8,less than or equal to 0.75, less than or equal to 0.7, less than orequal to 0.65, less than or equal to 0.6, less than or equal to 0.55,less than or equal to 0.5, less than or equal to 0.45, less than orequal to 0.4, less than or equal to 0.35, less than or equal to 0.3,less than or equal to 0.25, less than or equal to 0.2, less than orequal to 0.15, less than or equal to 0.1, less than or equal to 0.09,less than or equal to 0.08, less than or equal to 0.075, less than orequal to 0.07, less than or equal to 0.065, less than or equal to 0.06,less than or equal to 0.055, less than or equal to 0.05, less than orequal to 0.045, less than or equal to 0.04, or less than or equal to0.035. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.03 and less than or equal to 0.8,greater than or equal to 0.05 and less than or equal to 0.6, or greaterthan or equal to 0.07 and less than or equal to 0.5). Other ranges arealso possible. The ratio of peak height standard deviation to averagepeak height may be determined by finding the peak height standarddeviation and average peak height as described above, and then takingtheir ratio.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havean average peak spacing that is particularly advantageous. For instance,the plurality of peaks may have an average peak spacing of greater thanor equal to 1 mm, greater than or equal to 1.5 mm, greater than or equalto 2 mm, greater than or equal to 2.5 mm, greater than or equal to 3 mm,greater than or equal to 3.5 mm, greater than or equal to 4 mm, greaterthan or equal to 5 mm, greater than or equal to 6 mm, greater than orequal to 7 mm, greater than or equal to 8 mm, greater than or equal to 9mm, greater than or equal to 10 mm, greater than or equal to 12 mm,greater than or equal to 14 mm, greater than or equal to 16 mm, orgreater than or equal to 18 mm. In some embodiments, a filter mediacomprises a plurality of peaks having an average peak spacing of lessthan or equal to 20 mm, less than or equal to 18 mm, less than or equalto 16 mm, less than or equal to 14 mm, less than or equal to 12 mm, lessthan or equal to 10 mm, less than or equal to 9 mm, less than or equalto 8 mm, less than or equal to 7 mm, less than or equal to 6 mm, lessthan or equal to 5 mm, less than or equal to 4 mm, less than or equal to3.5 mm, less than or equal to 3 mm, less than or equal to 2.5 mm, lessthan or equal to 2 mm, or less than or equal to 1.5 mm. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 1 mm and less than or equal to 20 mm, greater than or equal to2 mm and less than or equal to 14 mm, or greater than or equal to 3 mmand less than or equal to 10 mm). Other ranges are also possible. Theaverage peak spacing may be determined by finding the spacing betweeneach peak and its two nearest neighbors by use of a scanning opticalmicroscope as described above, and then averaging these spacings toyield the average peak spacing.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havea peak spacing standard deviation that is particularly advantageous. Forinstance, the plurality of peaks may have a peak spacing standarddeviation of greater than or equal to 0.2 mm, greater than or equal to0.25 mm, greater than or equal to 0.3 mm, greater than or equal to 0.35mm, greater than or equal to 0.4 mm, greater than or equal to 0.45 mm,greater than or equal to 0.5 mm, greater than or equal to 0.6 mm,greater than or equal to 0.8 mm, greater than or equal to 1 mm, greaterthan or equal to 2 mm, greater than or equal to 3 mm, greater than orequal to 4 mm, greater than or equal to 5 mm, greater than or equal to 6mm, greater than or equal to 7 mm, greater than or equal to 8 mm, orgreater than or equal to 9 mm. In some embodiments, a filter mediacomprises a plurality of peaks having a peak spacing standard deviationof less than or equal to 10 mm, less than or equal to 9 mm, less than orequal to 8 mm, less than or equal to 7 mm, less than or equal to 6 mm,less than or equal to 5 mm, less than or equal to 4 mm, less than orequal to 3 mm, less than or equal to 2 mm, less than or equal to 1 mm,less than or equal to 0.8 mm, less than or equal to 0.6 mm, less than orequal to 0.5 mm, less than or equal to 0.45 mm, less than or equal to0.4 mm, less than or equal to 0.35 mm, less than or equal to 0.3 mm, orless than or equal to 0.25 mm. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 0.2 mm and lessthan or equal to 10 mm, greater than or equal to 0.3 mm and less than orequal to 7 mm, or greater than or equal to 0.4 mm and less than or equalto 4 mm). Other ranges are also possible. The peak spacing standarddeviation may be determined by finding the spacing between each peak andits two nearest neighbors by use of a scanning optical microscope asdescribed above, and then using standard statistical techniques todetermine the standard deviation of the nearest neighbor peak spacingsto yield the peak spacing standard deviation.

When a filter media comprises a plurality of peaks, such as a pluralityof peaks irregular in one or more ways, the plurality of peaks may havea ratio of peak spacing standard deviation to average peak spacing thatis particularly advantageous. For instance, the plurality of peaks mayhave a ratio of peak spacing standard deviation to average peak spacingof greater than or equal to 0.08, greater than or equal to 0.085,greater than or equal to 0.09, greater than or equal to 0.095, greaterthan or equal to 0.1, greater than or equal to 0.125, greater than orequal to 0.15, greater than or equal to 0.2, greater than or equal to0.25, greater than or equal to 0.3, greater than or equal to 0.35,greater than or equal to 0.4, greater than or equal to 0.45, greaterthan or equal to 0.5, greater than or equal to 0.6, greater than orequal to 0.7, greater than or equal to 0.8, or greater than or equal to0.9. In some embodiments, a filter media comprises a plurality of peakshaving a ratio of peak spacing standard deviation to average peakspacing of less than or equal to 1, less than or equal to 0.9, less thanor equal to 0.8, less than or equal to 0.7, less than or equal to 0.6,less than or equal to 0.5, less than or equal to 0.45, less than orequal to 0.4, less than or equal to 0.35, less than or equal to 0.3,less than or equal to 0.25, less than or equal to 0.2, less than orequal to 0.15, less than or equal to 0.1, less than or equal to 0.125,less than or equal to 0.1, less than or equal to 0.095, less than orequal to 0.09, or less than or equal to 0.085. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.08 and less than or equal to 1, greater than or equal to 0.15 andless than or equal to 0.8, or greater than or equal to 0.15 and lessthan or equal to 0.5). Other ranges are also possible. The ratio of peakspacing standard deviation to average peak spacing may be determined byfinding the peak spacing standard deviation and average peak spacing asdescribed above, and then taking their ratio.

The filter media described herein may have an advantageous averagesurface height. In some embodiments, a filter media comprises a layercomprising a plurality of peaks irregular in one or more ways having anadvantageous average surface height. In some embodiments, a filter media(and/or a layer therein comprising a plurality of irregular peaks) hasan average surface height of greater than or equal to 0.3 mm, greaterthan or equal to 0.5 mm, greater than or equal to 0.75 mm, greater thanor equal to 1 mm, greater than or equal to 1.5 mm, greater than or equalto 2 mm, greater than or equal to 2.5 mm, greater than or equal to 3 mm,greater than or equal to 4 mm, greater than or equal to 5 mm, greaterthan or equal to 6 mm, greater than or equal to 7 mm, greater than orequal to 8 mm, or greater than or equal to 9 mm. In some embodiments, afilter media (and/or a layer therein comprising a plurality of irregularpeaks) has an average surface height of less than or equal to 10 mm,less than or equal to 9 mm, less than or equal to 8 mm, less than orequal to 7 mm, less than or equal to 6 mm, less than or equal to 5 mm,less than or equal to 4 mm, less than or equal to 3 mm, less than orequal to 2.5 mm, less than or equal to 2 mm, less than or equal to 1.5mm, less than or equal to 1 mm, less than or equal to 0.75 mm, or lessthan or equal to 0.5 mm. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 0.3 mm and less than orequal to 10 mm, greater than or equal to 1 mm and less than or equal to8 mm, or greater than or equal to 3 mm and less than or equal to 7 mm).Other ranges are also possible. As used herein, the average surfaceheight of a filter media and/or a layer therein is the average of therelative heights of each point in the relative surface topography of afilter media and/or a layer therein after a selected amount ofcomputational processing. The relative surface topography of a filtermedia and/or a layer therein may be determined using scanning opticalmicroscopy as described above. Then, steps (1) and (2) of the processfor determining peak heights described above may be carried out toprocess the resultant data. Finally, the processed data may be averagedto yield an average surface height. If the layer having the averagesurface height in one or more of the ranges listed above is not on anexternal surface of the filter media (e.g., if it is covered by arelatively flat outer or cover layer), the layer or layers positionedexterior to the relevant layer may be removed so that the relevant layeris exposed, and average surface height of the exposed relevant layer maybe measured by optical microscopy as described above.

The filter media described herein may have a variety of suitable basisweights. The basis weight of a filter media will generally depend onwhether or not it is undulated and the size of the undulations. Forinstance, filter media comprising undulations on a single length scale(e.g., filter media that comprise a layer that has been gathered, suchas by the procedure shown in FIGS. 7A-7C, but not include an additionalstructure formed by, e.g., pleating or waving) typically have lowerbasis weights than filter media comprising undulations on two or morelength scales (e.g., filter media that comprise a layer that has beengathered, such as by the procedure shown in FIGS. 7A-7C, and alsocomprise an additional structure formed by, e.g., pleating or waving).

In some embodiments, a filter media comprising undulations on a singlelength scale has a basis weight of greater than or equal to 60 g/m²,greater than or equal to 70 g/m², greater than or equal to 80 g/m²,greater than or equal to 90 g/m², greater than or equal to 95 g/m²,greater than or equal to 100 g/m², greater than or equal to 110 g/m²,greater than or equal to 120 g/m², greater than or equal to 130 g/m², orgreater than or equal to 140 g/m². In some embodiments, a filter mediacomprising undulations on a single length scale has a basis weight ofless than or equal to 150 g/m², less than or equal to 140 g/m², lessthan or equal to 130 g/m², less than or equal to 120 g/m², less than orequal to 110 g/m², less than or equal to 100 g/m², less than or equal to95 g/m², less than or equal to 90 g/m², less than or equal to 80 g/m²,or less than or equal to 70 g/m². Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 60 g/m² andless than or equal to 150 g/m², greater than or equal to 70 g/m² andless than or equal to 140 g/m², or greater than or equal to 95 g/m² andless than or equal to 140 g/m²). Other ranges are also possible. Thebasis weight of a filter media may be determined by weighing a filtermedia of known area and then dividing the measured weight by the knownarea.

As described above, filter media comprising undulations on two or morelength scales may be provided. The ratio of the basis weight of a filtermedia after forming the undulations on the larger of the two lengthscales (e.g., by waving or pleating) to the basis weight of a filtermedia prior to forming the undulations on the larger of the two lengthscales may be referred to as the additional structure undulation ratio(which is equivalent to, e.g., the wave ratio for a waved media or thepleat ratio for a pleated media). A filter media comprising undulationson two or more length scales may have an additional structure undulationratio of greater than or equal to 1.5, greater than or equal to 1.75,greater than or equal to 2, greater than or equal to 2.25, greater thanor equal to 2.5, or greater than or equal to 2.75. A filter mediacomprising undulations on two or more length scales may have anadditional structure undulation ratio of less than or equal to 3, lessthan or equal to 2.75, less than or equal to 2.5, less than or equal to2.25, less than or equal to 2, or less than or equal to 1.75.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 1.5 and less than or equal to 3). Other rangesare also possible.

The filter media described herein may have a variety of suitablethicknesses. The thickness of a filter media will generally depend onwhether or not it is undulated and the size of the undulations. Forinstance, filter media comprising undulations on a single length scale(e.g., filter media that comprise a layer that has been gathered, suchas by the procedure shown in FIGS. 7A-7C, but not include an additionalstructure formed by, e.g., pleating or waving) typically have lowerthicknesses than filter media comprising undulations on two or morelength scales (e.g., filter media that comprise a layer that has beengathered, such as by the procedure shown in FIGS. 7A-7C, and alsocomprise an additional structure formed by pleating or waving). In someembodiments, a filter media comprising undulations on a single lengthscale has a thickness of greater than or equal to 2 mm, greater than orequal to 3 mm, greater than or equal to 4 mm, greater than or equal to 5mm, greater than or equal to 6 mm, greater than or equal to 7 mm, orgreater than or equal to 8 mm. In some embodiments, a filter mediacomprising undulations on a single length scale has a thickness of lessthan or equal to 10 mm, less than or equal to 8 mm, less than or equalto 7 mm, less than or equal to 6 mm, less than or equal to 5 mm, lessthan or equal to 4 mm, or less than or equal to 3 mm. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 2 mm and less than or equal to 10 mm, or greater than or equalto 3 mm and less than or equal to 7 mm). Other ranges are also possible.The thickness of a filter media may be determined by Edana WSP 120.1Standard (2005) with a pressure foot selected to have a 2 ounce load anda 1 square inch area. It should be understood that the values describedabove may also refer to thicknesses of filter media comprisingundulations on two or more length scales that have been extended to formfilter media comprising undulations on a single length scale. In someembodiments, the values of thickness above may be the thicknesses ofwaved or pleated filter media prior to waving or pleating.

As described above, filter media comprising undulations on two or morelength scales may be provided. These filter media may have thicknessesthat are defined by the undulations on the second length scale (e.g.,the wave height or pleat height). In some embodiments, a filter mediacomprising undulations on two or more length scales has a thickness ofgreater than or equal to 8 mm, greater than or equal to 10 mm, greaterthan or equal to 12.5 mm, greater than or equal to 15 mm, greater thanor equal to 20 mm, greater than or equal to 25 mm, greater than or equalto 30 mm, or greater than or equal to 40 mm. In some embodiments, afilter media comprising undulations on two or more length scales has athickness of less than or equal to 50 mm, less than or equal to 40 mm,less than or equal to 30 mm, less than or equal to 25 mm, less than orequal to 20 mm, less than or equal to 15 mm, less than or equal to 12.5mm, or less than or equal to 10 mm. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 8 mm and lessthan or equal to 50 mm). Other ranges are also possible. The thicknessof a filter media may be determined by Edana WSP 120.1 Standard (2005)with a pressure foot selected to have a 2 ounce load and a 1 square incharea.

The filter media described herein may have a variety of suitable meanflow pore sizes. In some embodiments, a filter media has a mean flowpore size of greater than or equal to 4 microns, greater than or equalto 5 microns, greater than or equal to 6 microns, greater than or equalto 7 microns, greater than or equal to 8 microns, greater than or equalto 10 microns, greater than or equal to 12 microns, greater than orequal to 14 microns, greater than or equal to 16 microns, greater thanor equal to 18 microns, greater than or equal to 20 microns, or greaterthan or equal to 22 microns. In some embodiments, a filter media has amean flow pore size of less than or equal to 25 microns, less than orequal to 22 microns, less than or equal to 20 microns, less than orequal to 18 microns, less than or equal to 16 microns, less than orequal to 14 microns, less than or equal to 12 microns, less than orequal to 10 microns, less than or equal to 8 microns, less than or equalto 7 microns, less than or equal to 6 microns, or less than or equal to5 microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 4 microns and less than or equal to 25microns, greater than or equal to 6 microns and less than or equal to 16microns, or greater than or equal to 7 microns and less than or equal to12 microns). Other ranges are also possible. The mean flow pore size ofa filter media may be determined in accordance with ASTM F316 (2011).

The filter media described herein may have a variety of suitablepressure drops. In some embodiments, a filter media has a pressure dropof greater than or equal to 0.2 mm H₂O, greater than or equal to 0.4 mmH₂O, greater than or equal to 0.6 mm H₂O, greater than or equal to 0.8mm H₂O, greater than or equal to 1 mm H₂O, greater than or equal to 1.2mm H₂O, greater than or equal to 1.4 mm H₂O, greater than or equal to1.6 mm H₂O, greater than or equal to 1.8 mm H₂O, greater than or equalto 2 mm H₂O, greater than or equal to 2.5 mm H₂O, greater than or equalto 3 mm H₂O, greater than or equal to 3.5 mm H₂O, greater than or equalto 4 mm H₂O, greater than or equal to 5 mm H₂O, greater than or equal to6 mm H₂O, or greater than or equal to 8 mm H₂O. In some embodiments, afilter media has a pressure drop of less than or equal to 10 mm H₂O,less than or equal to 8 mm H₂O, less than or equal to 6 mm H₂O, lessthan or equal to 5 mm H₂O, less than or equal to 4 mm H₂O, less than orequal to 3.5 mm H₂O, less than or equal to 3 mm H₂O, less than or equalto 2.5 mm H₂O, less than or equal to 2 mm H₂O, less than or equal to 1.8mm H₂O, less than or equal to 1.6 mm H₂O, less than or equal to 1.4 mmH₂O, less than or equal to 1.2 mm H₂O, less than or equal to 1 mm H₂O,less than or equal to 0.8 mm H₂O, less than or equal to 0.6 mm H₂O, orless than or equal to 0.4 mm H₂O. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 0.2 mm H₂O andless than or equal to 10 mm H₂O, greater than or equal to 0.4 mm H₂O andless than or equal to 6 mm H₂O, greater than or equal to 0.8 mm H₂O andless than or equal to 4 mm H₂O, or greater than or equal to 1.2 mm H₂Oand less than or equal to 1.8 mm H₂O). Other ranges are also possible.The pressure drop of a filter media may be determined by employing a TSI8130 Automated0 Filter Tester as described above with respect to themeasurement of gamma.

The filter media described herein may have a variety of initialpenetrations. In some embodiments, a filter media has an initialpenetration of less than or equal to 80%, less than or equal to 70%,less than or equal to 60%, less than or equal to 50%, less than or equalto 40%, less than or equal to 30%, less than or equal to 20%, less thanor equal to 15%, less than or equal to 10%, less than or equal to 5%,less than or equal to 2%, less than or equal to 1%, less than or equalto 0.5%, less than or equal to 0.2%, less than or equal to 0.1%, lessthan or equal to 0.05%, less than or equal to 0.02%, less than or equalto 0.01%, less than or equal to 0.005%, less than or equal to 0.002%,less than or equal to 0.001%, less than or equal to 0.0005%, less thanor equal to 0.0002%, or less than or equal to 0.0001%. In someembodiments, a filter media has an initial penetration of greater thanor equal to 0.00005%, greater than or equal to 0.0001%, greater than orequal to 0.0002%, greater than or equal to 0.0005%, greater than orequal to 0.001%, greater than or equal to 0.002%, greater than or equalto 0.005%, greater than or equal to 0.01%, greater than or equal to0.02%, greater than or equal to 0.05%, greater than or equal to 0.1%,greater than or equal to 0.2%, greater than or equal to 0.5%, greaterthan or equal to 1%, greater than or equal to 2%, greater than or equalto 5%, greater than or equal to 10%, greater than or equal to 15%,greater than or equal to 20%, greater than or equal to 30%, greater thanor equal to 40%, greater than or equal to 50%, greater than or equal to60%, or greater than or equal to 70%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.00005% and less than or equal to 80%). Other ranges are alsopossible. The initial penetration of a filter media may be determined byemploying a TSI 8130 Automated Filter Tester as described above withrespect to the measurement of gamma.

The filter media described herein may have a variety of suitable airpermeabilities. In some embodiments, a filter media has an airpermeability of greater than or equal to 20 CFM, greater than or equalto 25 CFM, greater than or equal to 30 CFM, greater than or equal to 35CFM, greater than or equal to 40 CFM, greater than or equal to 50 CFM,greater than or equal to 60 CFM, greater than or equal to 75 CFM,greater than or equal to 100 CFM, greater than or equal to 120 CFM,greater than or equal to 150 CFM, greater than or equal to 170 CFM,greater than or equal to 200 CFM, greater than or equal to 225 CFM,greater than or equal to 250 CFM, greater than or equal to 275 CFM,greater than or equal to 300 CFM, or greater than or equal to 325 CFM.In some embodiments, a filter media has an air permeability of less thanor equal to 350 CFM, less than or equal to 325 CFM, less than or equalto 300 CFM, less than or equal to 275 CFM, less than or equal to 250CFM, less than or equal to 225 CFM, less than or equal to 200 CFM, lessthan or equal to 170 CFM, less than or equal to 150 CFM, less than orequal to 120 CFM, less than or equal to 100 CFM, less than or equal to75 CFM, less than or equal to 60 CFM, less than or equal to 50 CFM, lessthan or equal to 40 CFM, less than or equal to 35 CFM, less than orequal to 30 CFM, or less than or equal to 25 CFM. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 20 CFM and less than or equal to 350 CFM, greater than or equal to 35CFM and less than or equal to 170 CFM, or greater than or equal to 20CFM and less than or equal to 350 CFM). Other ranges are also possible.The air permeability of a filter media may be determined in accordancewith ASTM Test Standard D737 (1996) under a pressure drop of 125 Pa on asample with a test area of 38 cm².

The filter media described herein may have a variety of suitable dustholding capacities. In some embodiments, a filter media has a dustholding capacity of greater than or equal to 60 g/m², greater than orequal to 70 g/m², greater than or equal to 80 g/m², greater than orequal to 90 g/m², greater than or equal to 100 g/m², greater than orequal to 110 g/m², greater than or equal to 135 g/m², greater than orequal to 150 g/m², greater than or equal to 162 g/m², or greater than orequal to 180 g/m². In some embodiments, a filter media has a dustholding capacity of less than or equal to 200 g/m², less than or equalto 180 g/m², less than or equal to 162 g/m², less than or equal to 150g/m², less than or equal to 135 g/m², less than or equal to 110 g/m²,less than or equal to 100 g/m², less than or equal to 90 g/m², less thanor equal to 80 g/m², or less than or equal to 70 g/m². Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 60 g/m² and less than or equal to 200 g/m², greater than orequal to 80 g/m² and less than or equal to 162 g/m², or greater than orequal to 90 g/m² and less than or equal to 135 g/m²). Other ranges arealso possible. The dust holding capacity of a filter media may bedetermined by the procedure described in ASHRAE 52.1 (1992) modifiedsuch that: (1) the filter media is weighed prior to the beginning of theprocedure and at the conclusion of the procedure, and (2) the mass ofdust held by the filter media is determined by subtracting the measuredmass of the filter media prior to the beginning of the procedure fromthe measured mass of the filter media at the conclusion of theprocedure. This procedure may be carried out by exposing a filter mediawith an area of 1 ft² to air comprising ASHRAE 52.1 synthetic test dustat a concentration of 2 g/100 ft³. The air comprising the test dust maybe provided to the filter media at a face velocity of 15 ft/min untilthe pressure drop of the filter media reaches 1.5 inches of H₂O. At thispoint, the procedure concludes and the mass of the filter media at theconclusion of the procedure may be determined by weighing.

As described above, some filter media described herein comprise morethan one layer. In some embodiments, a filter media comprises anefficiency layer. The efficiency layer may improve the efficiency of thefilter media. When present, the efficiency layer may be positioned in avariety of suitable locations in the filter media, such as theupstream-most layer, the downstream-most layer, or a layer for whichthere are both one or more layers positioned upstream and one or morelayers positioned downstream. In other words, it may be a first layer, asecond layer, a third layer, a fourth layer, or another layer. In someembodiments, a filter media comprises more than one efficiency layer.For instance, a filter media may comprise a first layer and a secondlayer that are efficiency layers, a first layer and a second layer thatare efficiency layers, a first layer and a third layer that areefficiency layers, or any other combination of layers that areefficiency layers.

Some efficiency layers described herein are fibrous. For instance, anefficiency layer may be a non-woven fiber web. The non-woven fiber webmay be a meltblown fiber web, an electrospun fiber web, a centrifugalspun fiber web, an air laid fiber web, a spunbond fiber web, or a cardednon-woven fiber web. Filter layers comprising two or more efficiencylayers may comprise efficiency layers that are all the same type offiber web (e.g., a filter media may comprise two efficiency layers thatare meltblown fiber webs), efficiency layers that are each differenttypes of fiber webs (e.g., a filter media may comprise a firstefficiency layer that is a meltblown fiber web and a second efficiencylayer that is an electrospun fiber web), or may comprise two or moreefficiency layers of a first type of fiber web and one or moreefficiency layers of a second type of fiber web different than the firsttype (e.g., a filter media may comprise two efficiency layers that aremeltblown fiber webs and one efficiency layer that is an electrospunfiber web).

Efficiency layers may comprise a variety of suitable types of fibers. Asdescribed above, an efficiency layer may comprise meltblown fibers,centrifugal spun fibers, electrospun fibers, and/or spunbond fibers. Insome embodiments, a filter media comprises an efficiency layercomprising synthetic fibers and/or natural fibers. Non-limiting examplesof synthetic fibers include polyolefin fibers (e.g., poly(propylene)fibers, poly(ethylene) fibers), polyester fibers (e.g., poly(butyleneterephthalate) fibers, poly(ethylene terephthalate) fibers), poly(amidefibers) (e.g., nylon 6 fibers, nylon 11 fibers), polycarbonate fibers,acrylic fibers, poly(4-methyl-1-pentene) fibers, polystyrene fibers,fluoropolymer fibers (e.g., poly(vinylidene fluoride) fibers),poly(ether sulfone) fibers, ethylene vinyl acetate fibers, ethylenevinyl alcohol fibers, poly(vinyl alcohol) fibers, poly(phenylenesulfide) fibers, and poly(lactic acid) fibers. One example of a naturalfiber is a chitosan fiber.

When present, an efficiency layer may comprise synthetic fibers having avariety of suitable average diameters. Each efficiency layer in thefilter media may independently comprise synthetic fibers having anaverage diameter of greater than or equal to 0.05 microns, greater thanor equal to 0.1 micron, greater than or equal to 0.2 microns, greaterthan or equal to 0.5 microns, greater than or equal to 1 micron, greaterthan or equal to 2 microns, greater than or equal to 3 microns, greaterthan or equal to 5 microns, or greater than or equal to 10 microns. Eachefficiency layer in the filter media may independently comprisesynthetic fibers having an average diameter of less than or equal to 12microns, less than or equal to 10 microns, less than or equal to 5microns, less than or equal to 3 microns, less than or equal to 2microns, less than or equal to 1 micron, less than or equal to 0.5microns, less than or equal to 0.2 microns, or less than or equal to 0.1micron. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.05 microns and less than or equal to12 microns, greater than or equal to 0.2 microns and less than or equalto 3 microns, or greater than or equal to 0.2 microns and less than orequal to 2 microns). Other ranges are also possible.

When present, an efficiency layer may comprise synthetic fibers having avariety of suitable average lengths. The fibers may comprise staplefibers and/or continuous fibers. Each efficiency layer in the filtermedia may independently comprise synthetic fibers having an averagelength of greater than or equal to 0.01 mm, greater than or equal to0.02 mm, greater than or equal to 0.05 mm, greater than or equal to 0.1mm, greater than or equal to 0.2 mm, greater than or equal to 0.5 mm,greater than or equal to 1 mm, greater than or equal to 2 mm, greaterthan or equal to 5 mm, greater than or equal to 10 mm, greater than orequal to 20 mm, greater than or equal to 50 mm, greater than or equal to90 mm, greater than or equal to 100 mm, greater than or equal to 200 mm,greater than or equal to 250 mm, greater than or equal to 300 mm,greater than or equal to 400 mm, greater than or equal to 500 mm,greater than or equal to 750 mm, greater than or equal to 1 m, greaterthan or equal to 2 m, greater than or equal to 5 m, greater than orequal to 10 m, greater than or equal to 20 m, greater than or equal to50 m, or greater than or equal to 100 m. Each efficiency layer in thefilter media may independently comprise synthetic fibers having anaverage length of less than or equal to 200 m, less than or equal to 100m, less than or equal to 50 m, less than or equal to 20 m, less than orequal to 10 m, less than or equal to 5 m, less than or equal to 2 m,less than or equal to 1 m, less than or equal to 750 mm, less than orequal to 500 mm, less than or equal to 400 mm, less than or equal to 300mm, less than or equal to 250 mm, less than or equal to 200 mm, lessthan or equal to 100 mm, less than or equal to 90 mm, less than or equalto 50 mm, less than or equal to 20 mm, less than or equal to 10 mm, lessthan or equal to 5 mm, less than or equal to 2 mm, less than or equal to1 mm, less than or equal to 0.5 mm, or less than or equal to 0.2 mm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.01 mm and less than or equal to 200 m,greater than or equal to 0.01 mm and less than or equal to 500 mm,greater than or equal to 50 mm and less than or equal to 300 mm, orgreater than or equal to 90 mm and less than or equal to 250 mm). Otherranges are also possible.

When present, an efficiency layer may have a variety of suitable basisweights. The basis weights of efficiency layers in which undulationshave yet to be formed tend to be lower than those that comprise one ormore sets of undulations. Forming undulations in an efficiency layertends to increase the amount of the efficiency layer per area of filtermedia footprint, and thus tends to increase the basis weight of theefficiency layer. As described above, fabrication of a filter media maycomprise forming undulations in an initially un-undulated efficiencylayer that then undergoes one or more processes to form one or more setsof undulations. For this reason, it may be more facile to refer to thebasis weights of efficiency layers prior to undulation. These basisweights are equivalent to the basis weights of the efficiency layers ifextended to remove all undulations therein.

Each efficiency layer in the filter media may independently have a basisweight prior to undulation of greater than or equal to 0.02 g/m²,greater than or equal to 0.05 g/m², greater than or equal to 0.1 g/m²,greater than or equal to 0.2 g/m², greater than or equal to 0.5 g/m²,greater than or equal to 1 g/m², greater than or equal to 2 g/m²,greater than or equal to 5 g/m², greater than or equal to 10 g/m²,greater than or equal to 20 g/m², greater than or equal to 30 g/m²,greater than or equal to 40 g/m², greater than or equal to 50 g/m², orgreater than or equal to 75 g/m². Each efficiency layer in the filtermedia may independently have a basis weight prior to undulation of lessthan or equal to 100 g/m², less than or equal to 75 g/m², less than orequal to 50 g/m², less than or equal to 40 g/m², less than or equal to30 g/m², less than or equal to 20 g/m², less than or equal to 10 g/m²,less than or equal to 5 g/m², less than or equal to 2 g/m², less than orequal to 1 g/m², less than or equal to 0.5 g/m², less than or equal to0.2 g/m², less than or equal to 0.1 g/m², or less than or equal to 0.05g/m². Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.02 g/m² and less than or equal to 100g/m², greater than or equal to 0.05 g/m² and less than or equal to 50g/m², or greater than or equal to 0.2 g/m² and less than or equal to 30g/m²). Other ranges are also possible.

As described above, efficiency layers comprising undulations on a singlelength scale may be provided. In some embodiments, an efficiency layercomprising undulations on a single length scale has a basis weight ofgreater than or equal to 0.08 g/m², greater than or equal to 0.1 g/m²,greater than or equal to 0.125 g/m², greater than or equal to 0.15 g/m²,greater than or equal to 0.2 g/m², greater than or equal to 0.25 g/m²,greater than or equal to 0.3 g/m², greater than or equal to 0.4 g/m²,greater than or equal to 0.5 g/m², greater than or equal to 0.75 g/m²,greater than or equal to 1 g/m², greater than or equal to 1.25 g/m²,greater than or equal to 1.5 g/m², greater than or equal to 2 g/m²,greater than or equal to 2.5 g/m², greater than or equal to 3 g/m²,greater than or equal to 4 g/m², greater than or equal to 5 g/m²,greater than or equal to 7.5 g/m², greater than or equal to 10 g/m²,greater than or equal to 12.5 g/m², greater than or equal to 15 g/m²,greater than or equal to 20 g/m², greater than or equal to 25 g/m²,greater than or equal to 30 g/m², greater than or equal to 40 g/m²,greater than or equal to 50 g/m², greater than or equal to 75 g/m²,greater than or equal to 100 g/m², greater than or equal to 125 g/m²,greater than or equal to 150 g/m², greater than or equal to 200 g/m²,greater than or equal to 250 g/m², greater than or equal to 300 g/m²,greater than or equal to 400 g/m², or greater than or equal to 500 g/m².In some embodiments, an efficiency layer comprising undulations on asingle length scale has a basis weight of less than or equal to 500g/m², less than or equal to 400 g/m², less than or equal to 300 g/m²,less than or equal to 250 g/m², less than or equal to 200 g/m², lessthan or equal to 150 g/m², less than or equal to 125 g/m², less than orequal to 100 g/m², less than or equal to 75 g/m², less than or equal to50 g/m², less than or equal to 40 g/m², less than or equal to 30 g/m²,less than or equal to 25 g/m², less than or equal to 20 g/m², less thanor equal to 15 g/m², less than or equal to 12.5 g/m², less than or equalto 10 g/m², less than or equal to 7.5 g/m², less than or equal to 5g/m², less than or equal to 4 g/m², less than or equal to 3 g/m², lessthan or equal to 2.5 g/m², less than or equal to 2 g/m², less than orequal to 1.5 g/m², less than or equal to 1.25 g/m², less than or equalto 1 g/m², less than or equal to 0.75 g/m², less than or equal to 0.5g/m², less than or equal to 0.4 g/m², less than or equal to 0.3 g/m²,less than or equal to 0.25 g/m², less than or equal to 0.2 g/m², lessthan or equal to 0.15 g/m², less than or equal to 0.125 g/m², or lessthan or equal to 0.1 g/m². Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0.08 g/m² and lessthan or equal to 500 g/m², greater than or equal to 0.2 g/m² and lessthan or equal to 250 g/m², or greater than or equal to 0.8 g/m² and lessthan or equal to 150 g/m²). Other ranges are also possible. If a filtermedia comprises two or more efficiency layers comprising undulations ona single length scale, each efficiency layer may independently have abasis weight in one or more of the ranges listed above.

When present, an efficiency layer may have a variety of suitablethicknesses. As described above with respect to the basis weight of theefficiency layer, the thicknesses of the efficiency layers that in whichundulations have yet to be formed tend to be lower than those thatcomprise one or more sets of undulations. As described above,fabrication of a filter media may comprise forming undulations in aninitially un-undulated efficiency layer that then undergoes one or moreprocesses to form one or more sets of undulations. For this reason, itmay be more facile to refer to the thicknesses of efficiency layersprior to undulation. These thicknesses are equivalent to the thicknessesof the efficiency layers if extended to remove all undulations therein

Each efficiency layer in the filter media may independently have athickness prior to undulation of greater than or equal to 0.001 mm,greater than or equal to 0.002 mm, greater than or equal to 0.005 mm,greater than or equal to 0.01 mm, greater than or equal to 0.02 mm,greater than or equal to 0.05 mm, greater than or equal to 0.075 mm,greater than or equal to 0.1 mm, greater than or equal to 0.13 mm,greater than or equal to 0.2 mm, greater than or equal to 0.3 mm,greater than or equal to 0.4 mm, greater than or equal to 0.5 mm,greater than or equal to 0.7 mm, greater than or equal to 1 mm, greaterthan or equal to 1.25 mm, greater than or equal to 1.5 mm, greater thanor equal to 1.75 mm, greater than or equal to 2 mm, or greater than orequal to 2.25 mm. Each efficiency layer in the filter media mayindependently have a thickness prior to undulation of less than or equalto 2.5 mm, less than or equal to 2.25 mm, less than or equal to 2 mm,less than or equal to 1.75 mm, less than or equal to 1.5 mm, less thanor equal to 1.25 mm, less than or equal to 1 mm, less than or equal to0.7 mm, less than or equal to 0.5 mm, less than or equal to 0.4 mm, lessthan or equal to 0.3 mm, less than or equal to 0.2 mm, less than orequal to 0.13 mm, less than or equal to 0.1 mm, less than or equal to0.075 mm, less than or equal to 0.05 mm, less than or equal to 0.02 mm,less than or equal to 0.01 mm, less than or equal to 0.005 mm, or lessthan or equal to 0.002 mm. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0.001 mm and less thanor equal to 2.5 mm, greater than or equal to 0.01 mm and less than orequal to 2.5 mm, greater than or equal to 0.1 mm and less than or equalto 0.7 mm, or greater than or equal to 0.13 mm and less than or equal to0.3 mm). Other ranges are also possible.

As described above, efficiency layers comprising undulations on a singlelength scale may be provided. In some embodiments, an efficiency layercomprising undulations on a single length scale has a thickness ofgreater than or equal to 1.5 mm, greater than or equal to 2 mm, greaterthan or equal to 2.5 mm, greater than or equal to 3 mm, greater than orequal to 4 mm, greater than or equal to 5 mm, greater than or equal to7.5 mm, greater than or equal to 10 mm, or greater than or equal to 12.5mm. In some embodiments, an efficiency layer comprising undulations on asingle length scale has a thickness of less than or equal to 15 mm, lessthan or equal to 12.5 mm, less than or equal to 10 mm, less than orequal to 7.5 mm, less than or equal to 5 mm, less than or equal to 4 mm,less than or equal to 3 mm, less than or equal to 2.5 mm, or less thanor equal to 2 mm. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 1.5 mm and less than or equalto 15 mm). Other ranges are also possible. If a filter media comprisestwo or more efficiency layers comprising undulations on a single lengthscale, each efficiency layer may independently have a thickness in oneor more of the ranges listed above.

The thickness of efficiency layers with thicknesses of less than orequal to 0.025 mm may be determined by cross-sectional SEM. Thethickness of efficiency layers with thicknesses of greater than 0.025 mmmay be determined by Edana WSP 120.1 Standard (2005) with a pressurefoot selected to have a 2 ounce load and a 1 square inch area.

When present, an efficiency layer may have a variety of suitable meanflow pore sizes. Each efficiency layer in the filter media mayindependently have a mean flow pore size of greater than or equal to 2microns, greater than or equal to 5 microns, greater than or equal to 6microns, greater than or equal to 7 microns, greater than or equal to 8microns, greater than or equal to 9 microns, greater than or equal to 10microns, greater than or equal to 11 microns, greater than or equal to12 microns, greater than or equal to 13 microns, greater than or equalto 14 microns, greater than or equal to 15 microns, greater than orequal to 17.5 microns, greater than or equal to 20 microns, or greaterthan or equal to 22.5 microns. Each efficiency layer in the filter mediamay independently have a mean flow pore size of less than or equal to 25microns, less than or equal to 22.5 microns, less than or equal to 20microns, less than or equal to 17.5 microns, less than or equal to 15microns, less than or equal to 14 microns, less than or equal to 13microns, less than or equal to 12 microns, less than or equal to 11microns, less than or equal to 10 microns, less than or equal to 9microns, less than or equal to 8 microns, less than or equal to 7microns, less than or equal to 6 microns, or less than or equal to 5microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 2 microns and less than or equal to 25microns, greater than or equal to 5 microns and less than or equal to 15microns, or greater than or equal to 7 microns and less than or equal to12 microns). Other ranges are also possible. The mean flow pore size ofan efficiency layer may be determined in accordance with ASTM F316(2011).

When present, an efficiency layer may have a variety of suitablesolidities. Each efficiency layer in the filter media may independentlyhave a solidity of greater than or equal to 0.5%, greater than or equalto 1%, greater than or equal to 1.5%, greater than or equal to 2%,greater than or equal to 2.5%, greater than or equal to 3%, greater thanor equal to 3.5%, greater than or equal to 4%, greater than or equal to5%, greater than or equal to 6%, greater than or equal to 7%, greaterthan or equal to 8%, or greater than or equal to 10%. Each efficiencylayer in the filter media may independently have a solidity of less thanor equal to 12%, less than or equal to 10%, less than or equal to 8%,less than or equal to 7%, less than or equal to 6%, less than or equalto 5%, less than or equal to 4%, less than or equal to 3.5%, less thanor equal to 3%, less than or equal to 2.5%, less than or equal to 2%,less than or equal to 1.5%, or less than or equal to 1%. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 0.5% and less than or equal to 12%, greater than or equal to 2%and less than or equal to 8%, or greater than or equal to 2.5% and lessthan or equal to 6%). Other ranges are also possible.

The solidity of an efficiency layer may be determined by using thefollowing formula: solidity=[basis weight/(fiberdensity*thickness)]*100%. The basis weight and thickness may bedetermined as described elsewhere herein. The fiber density isequivalent to the average density of the material or material(s) formingthe fiber, which is typically specified by the fiber manufacturer. Theaverage density of the materials forming the fibers may be determinedby: (1) determining the total volume of all of the fibers in the filtermedia; and (2) dividing the total mass of all of the fibers in thefilter media by the total volume of all of the fibers in the filtermedia. If the mass and density of each type of fiber in the filter mediaare known, the volume of all the fibers in the filter media may bedetermined by: (1) for each type of fiber, dividing the total mass ofthe type of fiber in the filter media by the density of the type offiber; and (2) summing the volumes of each fiber type. If the mass anddensity of each type of fiber in the filter media are not known, thevolume of all the fibers in the filter media may be determined inaccordance with Archimedes' principle.

When present, an efficiency layer may have a variety of suitablestiffnesses. In some embodiments, an efficiency layer is a layer with arelatively low stiffness. Each efficiency layer in the filter media mayindependently have a stiffness of greater than or equal to 1 mg, greaterthan or equal to 2 mg, greater than or equal to 3 mg, greater than orequal to 4 mg, greater than or equal to 5 mg, greater than or equal to 6mg, greater than or equal to 8 mg, greater than or equal to 10 mg,greater than or equal to 15 mg, greater than or equal to 20 mg, greaterthan or equal to 25 mg, greater than or equal to 30 mg, greater than orequal to 40 mg, greater than or equal to 50 mg, or greater than or equalto 75 mg. Each efficiency layer in the filter media may independentlyhave a stiffness of less than or equal to 100 mg, less than or equal to75 mg, less than or equal to 50 mg, less than or equal to 40 mg, lessthan or equal to 30 mg, less than or equal to 25 mg, less than or equalto 20 mg, less than or equal to 15 mg, less than or equal to 10 mg, lessthan or equal to 8 mg, less than or equal to 6 mg, less than or equal to5 mg, less than or equal to 4 mg, less than or equal to 3 mg, or lessthan or equal to 2 mg. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 1 mg and less than orequal to 100 mg, greater than or equal to 1 mg and less than or equal to50 mg, greater than or equal to 3 mg and less than or equal to 30 mg, orgreater than or equal to 5 mg and less than or equal to 10 mg). Otherranges are also possible. The stiffness of an efficiency layer may bedetermined in accordance with WSP 90.2 (2015).

When present, an efficiency layer may have a variety of suitablepressure drops. Each efficiency layer in the filter media mayindependently have a pressure drop of greater than or equal to 0.5 mmH₂O, greater than or equal to 0.75 mm H₂O, greater than or equal to 1 mmH₂O, greater than or equal to 1.2 mm H₂O, greater than or equal to 1.5mm H₂O, greater than or equal to 2 mm H₂O, greater than or equal to 2.5mm H₂O, greater than or equal to 3 mm H₂O, greater than or equal to 3.5mm H₂O, greater than or equal to 4 mm H₂O, greater than or equal to 5 mmH₂O, greater than or equal to 6 mm H₂O, greater than or equal to 7 mmH₂O, greater than or equal to 8 mm H₂O, or greater than or equal to 10mm H₂O. Each efficiency layer in the filter media may independently havea pressure drop of less than or equal to 12 mm H₂O, less than or equalto 10 mm H₂O, less than or equal to 8 mm H₂O, less than or equal to 7 mmH₂O, less than or equal to 6 mm H₂O, less than or equal to 5 mm H₂O,less than or equal to 4 mm H₂O, less than or equal to 3.5 mm H₂O, lessthan or equal to 3 mm H₂O, less than or equal to 2.5 mm H₂O, less thanor equal to 2 mm H₂O, less than or equal to 1.5 mm H₂O, less than orequal to 1.2 mm H₂O, less than or equal to 1 mm H₂O, or less than orequal to 0.75 mm H₂O. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 0.5 mm H₂O and less thanor equal to 12 mm H₂O, greater than or equal to 1 mm H₂O and less thanor equal to 7 mm H₂O, or greater than or equal to 1.2 mm H₂O and lessthan or equal to 3.5 mm H₂O). The pressure drop of an efficiency layermay be determined by employing a TSI 8130 Automated Filter Tester asdescribed above with respect to the measurement of gamma.

When present, an efficiency layer may have a variety of suitable airpermeabilities. Each efficiency layer in the filter media mayindependently have an air permeability of greater than or equal to 2CFM, greater than or equal to 5 CFM, greater than or equal to 10 CFM,greater than or equal to 15 CFM, greater than or equal to 20 CFM,greater than or equal to 30 CFM, greater than or equal to 40 CFM,greater than or equal to 50 CFM, greater than or equal to 70 CFM,greater than or equal to 90 CFM, greater than or equal to 100 CFM,greater than or equal to 120 CFM, greater than or equal to 150 CFM,greater than or equal to 175 CFM, greater than or equal to 200 CFM, orgreater than or equal to 225 CFM. Each efficiency layer in the filtermedia may independently have an air permeability of less than or equalto 250 CFM, less than or equal to 225 CFM, less than or equal to 200CFM, less than or equal to 175 CFM, less than or equal to 150 CFM, lessthan or equal to 120 CFM, less than or equal to 100 CFM, less than orequal to 90 CFM, less than or equal to 70 CFM, less than or equal to 50CFM, less than or equal to 40 CFM, less than or equal to 30 CFM, lessthan or equal to 20 CFM, less than or equal to 15 CFM, less than orequal to 10 CFM, or less than or equal to 5 CFM. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 2 CFM and less than or equal to 250 CFM, greater than or equal to 20CFM and less than or equal to 120 CFM, or greater than or equal to 40CFM and less than or equal to 90 CFM). Other ranges are also possible.The air permeability of an efficiency layer may be determined inaccordance with ASTM Test Standard D737 (1996) under a pressure drop of125 Pa on a sample with a test area of 38 cm².

When present, an efficiency layer may be charged or may be uncharged. Insome embodiments, a filter media comprises at least one chargedefficiency layer and at least one uncharged efficiency layer. In someembodiments, a filter media comprises an efficiency layer that is acharged meltblown fiber web. Charge may be induced on the efficiencylayer by a variety of suitable charging process, non-limiting examplesof which include an electrostatic charging process, a triboelectriccharging process, and a hydro charging process. In some embodiments, afilter media comprises a charged electrospun efficiency layer whichacquired its charge during electro spinning.

A hydro charging process may comprise impinging jets and/or streams ofwater droplets onto an initially uncharged efficiency layer to cause itto become charged electrostatically. At the conclusion of the hydrocharging process, the efficiency layer may have an electret charge. Thejets and/or streams of water droplets may impinge on the efficiencylayer at a variety of suitable pressures, such as a pressure of between10 to 50 psi, and may be provided by a variety of suitable sources, suchas a sprayer. In some embodiments, an efficiency layer is hydro chargedby using an apparatus that may be employed for the hydroentanglement offibers which is operated at a lower pressure than is typical for thehydroentangling process. The water impinging on the efficiency layer maybe relatively pure; for instance, it may be distilled water and/ordeionized water. After electrostatic charging in this manner, theefficiency layer may be dried, such as with air dryer.

In some embodiments, an efficiency layer is hydro charged while beingmoved laterally. The efficiency layer may be transported on a porousbelt, such as a screen or mesh-type conveyor belt. As it is beingtransported on the porous belt, it may be exposed to a spray and/or jetsof water pressurized by a pump. The water jets and/or spray may impingeon the efficiency layer and/or penetrate therein. In some embodiments, avacuum is provided beneath the porous transport belt, which may aid thepassage of water through the efficiency layer and/or reduce the amountof time and energy necessary for drying the efficiency layer at theconclusion of the hydro charging process.

As described above, some filter media herein comprise a layer that is ascrim. Some filter media comprise two or more layers that are scrims.The scrim(s) may be a layer that is fairly open. For instance, thescrim(s) may have a relatively high air permeability (e.g., in excess of1000 CFM) and/or a relatively low pressure drop (e.g., a pressure dropthat does not contribute appreciably to the pressure drop of the filtermedia as a whole). A filter media may comprise a scrim that supports oneor more other layers (e.g., one or more efficiency layers and/or one ormore nanofiber layers) while not adding appreciably to the pressure dropof the filter media. Some scrims may be layers that are capable ofundergoing a reversible stretch. In some embodiments, as also describedabove, a filter media comprises a scrim that holds one or more otherlayers (e.g., one or more efficiency layers and/or one or more nanofiberlayers) in a manner such that the filter media comprises a plurality ofpeaks that are irregular in one or more ways. For instance, it may holdone or more other layers such that they are undulated and theundulations are irregular in one or more ways. Some filter media maycomprise a scrim that protects one or more layers of a filter media,such as one or more layers of a filter media held by another scrim in amanner such that the filter media comprises a plurality of peaks thatare irregular in one or more ways. Some scrims may be positionedadjacent to an efficiency layer and/or may be adhered to an efficiencylayer by an adhesive.

A variety of suitable scrims may be employed in the filter mediadescribed herein. In some embodiments, a filter media comprises a scrimthat is fibrous. For instance, a filter media may comprise a scrim thatis a non-woven fiber web, such as a spunbond fiber web. As anotherexample, a filter media may comprise a scrim that is a mesh, such as anextruded mesh. As a third example, a filter media may comprise a scrimthat is a woven material. In some embodiments, a scrim may compriseelastically extensible fibers that are not in direct contact with eachother. The scrim or scrims may be cut from a material hundreds of yardsin length wound around a roll and/or from a creel.

When a filter media comprises a spunbond scrim, the spunbond scrim maycomprise a variety of suitable types of spunbond fibers. A spunbondscrim may comprise fibers that are synthetic fibers, such as polyolefinfibers (e.g., poly(propylene) fibers), polyester fibers, and/or nylonfibers.

When a filter media comprises a spunbond scrim, the spunbond scrim maycomprise fibers having a variety of suitable average diameters. Thespunbond scrim may comprise fibers having an average diameter of greaterthan or equal to 1 micron, greater than or equal to 2 microns, greaterthan or equal to 5 microns, greater than or equal to 7.5 microns,greater than or equal to 10 microns, greater than or equal to 12.5microns, greater than or equal to 15 microns, greater than or equal to20 microns, greater than or equal to 25 microns, greater than or equalto 30 microns, greater than or equal to 35 microns, greater than orequal to 40 microns, or greater than or equal to 45 microns. Thespunbond scrim may comprise fibers having an average diameter of lessthan or equal to 50 microns, less than or equal to 45 microns, less thanor equal to 40 microns, less than or equal to 35 microns, less than orequal to 30 microns, less than or equal to 25 microns, less than orequal to 20 microns, less than or equal to 15 microns, less than orequal to 12.5 microns, less than or equal to 10 microns, less than orequal to 7.5 microns, less than or equal to 5 microns, or less than orequal to 2 microns. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 1 micron and less than or equalto 50 microns, or greater than or equal to 15 microns and less than orequal to 35 microns). Other ranges are also possible.

When a filter media comprises a spunbond scrim, the fibers therein maybe continuous.

In some embodiments, a scrim (e.g., a mesh scrim, a non-woven scrim, awoven scrim, a scrim comprising elastically extensible fibers that arenot in direct contact with each other) comprises fibers that areelastically extensible. In other words, the scrim may comprise fibersthat can be stretched to a relatively high elongation without breakingand then allowed to recover to a length close to or identical to theirlength prior to being stretched. This may be advantageous for scrimscapable of undergoing a reversible stretch, such as scrims onto whichone or more other layers are deposited when the scrim is in a reversiblystretched state. Some elastically extensible fibers may be capable ofbeing stretched up to 1.5 times their initial length without breakingand may then recover to a length close to or identical to their lengthprior to being stretched. In some embodiments, a scrim compriseselastically extensible fibers capable of being stretched up to 1.75, 2,2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8,8.5, 9, 9.5, or 10 times their initial length without breaking and maythen recover to a length close to or identical to their length prior tobeing stretched. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 1 and less than or equal to10). Other ranges are also possible.

Non-limiting examples of suitable elastically extensible fibers includefibers comprising elastomeric materials, such as fibers comprising blockcopolymers (e.g., block copolymers comprising styrene, such as Kraton)and fibers comprising polyurethane elastomers (e.g., Spandex fibers).

When present, a scrim may comprise elastically extensible fibers havinga variety of suitable average diameters. A scrim may compriseelastically extensible fibers having an average diameter of greater thanor equal to 0.2 mm, greater than or equal to 0.25 mm, greater than orequal to 0.3 mm, greater than or equal to 0.35 mm, greater than or equalto 0.4 mm, greater than or equal to 0.5 mm, greater than or equal to 0.6mm, greater than or equal to 0.7 mm, greater than or equal to 0.8 mm,greater than or equal to 1 mm, or greater than or equal to 1.5 mm. Ascrim may comprise elastically extensible fibers having an averagediameter of less than or equal to 2 mm, less than or equal to 1.5 mm,less than or equal to 1 mm, less than or equal to 0.8 mm, less than orequal to 0.7 mm, less than or equal to 0.6 mm, less than or equal to 0.5mm, less than or equal to 0.4 mm, less than or equal to 0.35 mm, lessthan or equal to 0.3 mm, or less than or equal to 0.25 mm. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to 0.2 mm and less than or equal to 2 mm, greater than or equal to0.3 mm and less than or equal to 2 mm, or greater than or equal to 0.3mm and less than 0.8 mm). Other ranges are also possible.

When present, a scrim may comprise elastically extensible fibers havinga variety of suitable average lengths. A scrim may comprise elasticallyextensible fibers having an average length of greater than or equal to 5mm, greater than or equal to 10 mm, greater than or equal to 20 mm,greater than or equal to 50 mm, greater than or equal to 100 mm, greaterthan or equal to 200 mm, greater than or equal to 500 mm, greater thanor equal to 1 m, greater than or equal to 2 m, greater than or equal to5 m, greater than or equal to 10 m, greater than or equal to 20 m,greater than or equal to 50 m, or greater than or equal to 100 m. Insome embodiments, the elastically extensible fibers may be continuousfibers. A scrim may comprise elastically extensible fibers having anaverage length of less than or equal to 200 m, less than or equal to 100m, less than or equal to 50 m, less than or equal to 20 m, less than orequal to 10 m, less than or equal to 5 m, less than or equal to 2 m,less than or equal to 1 m, less than or equal to 750 mm, less than orequal to 500 mm, less than or equal to 400 mm, less than or equal to 300mm, less than or equal to 250 mm, less than or equal to 200 mm, lessthan or equal to 100 mm, less than or equal to 90 mm, less than or equalto 50 mm, less than or equal to 20 mm, or less than or equal to 10 mm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 5 mm and less than or equal to 100 m). Otherranges are also possible. The elastically extensible fibers may extendthroughout a source of the scrim, such as a throughout a material roundaround a roll or forming a creel.

As described above, some scrims may be relatively extensible. Whenpresent, a scrim as a whole may be capable of being stretched to arelatively high elongation without breaking and then allowed to recoverto a length close to or identical to its length prior to beingstretched. In some embodiments, a scrim may be capable of undergoing areversible stretch of greater than or equal to 50%, greater than orequal to 75%, greater than or equal to 100%, greater than or equal to125%, greater than or equal to 150%, greater than or equal to 175%,greater than or equal to 200%, greater than or equal to 225%, greaterthan or equal to 250%, greater than or equal to 275%, greater than orequal to 300%, greater than or equal to 325%, greater than or equal to350%, greater than or equal to 375%, greater than or equal to 400%,greater than or equal to 450%, greater than or equal to 500%, greaterthan or equal to 600%, or greater than or equal to 800%. In someembodiments, a scrim may be capable of undergoing a reversible stretchof less than or equal to 1000%, less than or equal to 800%, less than orequal to 600%, less than or equal to 500%, less than or equal to 450%,less than or equal to 400%, less than or equal to 375%, less than orequal to 350%, less than or equal to 325%, less than or equal to 300%,less than or equal to 275%, less than or equal to 250%, less than orequal to 225%, less than or equal to 200%, less than or equal to 175%,less than or equal to 150%, less than or equal to 125%, less than orequal to 100%, or less than or equal to 75%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 50% and less than or equal to 1000%, greater than or equal to 100%and less than or equal to 400%, or greater than or equal to 200% andless than or equal to 300%). Other ranges are also possible.

When present, a scrim may have a variety of suitable basis weights. Thebasis weights of scrims that in which undulations have yet to be formedtend to be lower than those that comprise one or more sets ofundulations. Forming undulations in a scrim tends to increase the amountof the scrim per area of filter media footprint, and thus tends toincrease the basis weight of the scrim. As described above, fabricationof a filter media may comprise forming undulations in an initiallyun-undulated scrim that then undergoes one or more processes to form oneor more sets of undulations. For this reason, it may be more facile torefer to the basis weights of scrims prior to undulation. These basisweights are equivalent to the basis weights of the scrims if extended toremove all undulations therein.

A scrim may have a basis weight prior to undulation of greater than orequal to 5 g/m², greater than or equal to 7.5 g/m², greater than orequal to 10 g/m², greater than or equal to 15 g/m², greater than orequal to 20 g/m², greater than or equal to 25 g/m², greater than orequal to 30 g/m², greater than or equal to 40 g/m², greater than orequal to 50 g/m², greater than or equal to 60 g/m², greater than orequal to 70 g/m², greater than or equal to 80 g/m², or greater than orequal to 100 g/m². A scrim may have a basis weight prior to undulationof less than or equal to 120 g/m², less than or equal to 100 g/m², lessthan or equal to 80 g/m², less than or equal to 70 g/m², less than orequal to 60 g/m², less than or equal to 50 g/m², less than or equal to40 g/m², less than or equal to 30 g/m², less than or equal to 25 g/m²,less than or equal to 20 g/m², less than or equal to 15 g/m², less thanor equal to 10 g/m², or less than or equal to 7.5 g/m². Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 5 g/m² and less than or equal to 120 g/m², greater than orequal to 20 g/m² and less than or equal to 80 g/m², or greater than orequal to 40 g/m² and less than or equal to 60 g/m²). Other ranges arealso possible. The basis weight of a scrim may be determined by weighinga scrim of known area and then dividing the measured weight by the knownarea.

When present, a scrim may have a variety of suitable thicknesses. Thethicknesses of scrims in which undulations have yet to be formed, tendto be lower than those that comprise one or more sets of undulations. Asdescribed above, fabrication of a filter media may comprise formingundulations in an initially un-undulated scrim that then undergoes oneor more processes to form one or more sets of undulations. For thisreason, it may be more facile to refer to the thicknesses of scrimsprior to undulation. These thicknesses are equivalent to the thicknessesof the scrims if extended to remove all undulations therein

A scrim may have a thickness prior to undulation of greater than orequal to 0.1 mm, greater than or equal to 0.15 mm, greater than or equalto 0.2 mm, greater than or equal to 0.25 mm, greater than or equal to0.3 mm, greater than or equal to 0.35 mm, greater than or equal to 0.4mm, greater than or equal to 0.45 mm, greater than or equal to 0.5 mm,greater than or equal to 0.55 mm, greater than or equal to 0.6 mm,greater than or equal to 0.65 mm, greater than or equal to 0.7 mm,greater than or equal to 0.8 mm, greater than or equal to 0.9 mm,greater than or equal to 1 mm, greater than or equal to 1.5 mm, greaterthan or equal to 2 mm, greater than or equal to 3 mm, or greater than orequal to 4 mm. A scrim may have a thickness prior to undulation of lessthan or equal to 5 mm, less than or equal to 4 mm, less than or equal to3 mm, less than or equal to 2 mm, less than or equal to 1.5 mm, lessthan or equal to 1 mm, less than or equal to 0.9 mm, less than or equalto 0.8 mm, less than or equal to 0.7 mm, less than or equal to 0.65 mm,less than or equal to 0.6 mm, less than or equal to 0.55 mm, less thanor equal to 0.5 mm, less than or equal to 0.45 mm, less than or equal to0.4 mm, less than or equal to 0.35 mm, less than or equal to 0.3 mm,less than or equal to 0.25 mm, less than or equal to 0.2 mm, or lessthan or equal to 0.15 mm. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0.1 mm and less thanor equal to 5 mm, greater than or equal to 0.3 mm and less than or equalto 1 mm, or greater than or equal to 0.4 mm and less than or equal to0.6 mm). The thickness of a scrim may be determined by Edana WSP 120.1Standard (2005) with a pressure foot selected to have a 2 ounce load anda 1 square inch area.

As described above, some scrims may be relatively open. When present, ascrim may comprise openings that may be parametrized by a longest linethat has endpoints on the outer boundary of the opening and passes overthe opening. This line would be equivalent to a diameter for a circularopening or to a diagonal for a rectangular opening. In some embodiments,a scrim comprises openings having a longest line that has endpoints onthe outer boundary of the opening and passes over the opening of greaterthan or equal to 0.1 inch, greater than or equal to 0.15 inches, greaterthan or equal to 0.2 inches, greater than or equal to 0.25 inches,greater than or equal to 0.3 inches, greater than or equal to 0.35inches, greater than or equal to 0.4 inches, or greater than or equal to0.45 inches. A scrim may comprise openings having a longest line thathas endpoints on the outer boundary of the opening and passes over theopening of less than or equal to 0.5 inches, less than or equal to 0.45inches, less than or equal to 0.4 inches, less than or equal to 0.35inches, less than or equal to 0.3 inches, less than or equal to 0.25inches, less than or equal to 0.2 inches, or less than or equal to 0.15inches. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.1 inch and less than or equal to 0.5inches). Other ranges are also possible. The openings may have a varietyof shapes (e.g., square, rectangular, and the like).

As described above, some filter media comprise a nanofiber layer. Thenanofiber layer may improve the filtration performance of the filtermedia. In some embodiments, a nanofiber layer functions as an efficiencylayer. In such cases, the nanofiber layer may have one or moreproperties described herein with respect to efficiency layers and/or mayhave one or more properties described herein with respect to nanofiberlayers. When present, the nanofiber layer may be positioned in a varietyof suitable locations in the filter media, such as the upstream-mostlayer, the downstream-most layer, or a layer for which there are bothone or more layers positioned upstream and one or more layers positioneddownstream. In other words, it may be a first layer, a second layer, athird layer, a fourth layer, or another layer. In some embodiments, afilter media comprises more than one nanofiber layer. For instance, afilter media may comprise a first layer and a second layer that arenanofiber layers, a second layer and a third layer that are nanofiberlayers, a first layer and a third layer that are nanofiber layers, orany other combination of layers that are nanofiber layers. In someembodiments, a filter media comprises a nanofiber layer and a scrimlayer positioned on opposite sides of another efficiency layer (e.g., ameltblown efficiency layer, another nanofiber efficiency layer).

Some nanofiber layers described herein are fibrous. For instance, ananofiber layer may be a non-woven fiber web. In some embodiments, thenon-woven fiber web is an electrospun fiber web, a meltblown fiber web,or a centrifugal spun fiber web and/or comprises electrospun fibers,meltblown fibers, and/or centrifugal spun fibers. A nanofiber layer maycomprise synthetic fibers and/or natural fibers. Non-limiting examplesof synthetic fibers include nylon fibers (e.g., nylon 6 fibers),poly(vinylidene fluoride) fibers, poly(ether sulfone) fibers, polyesterfibers, polycarbonate fibers, and/or poly(lactic acid) fibers. Oneexample of a natural fiber is a chitosan fiber.

When present, a nanofiber layer may comprise synthetic fibers having avariety of suitable average diameters. Each nanofiber layer in thefilter media may independently comprise synthetic fibers having anaverage diameter of greater than or equal to 20 nm, greater than orequal to 50 nm, greater than or equal to 75 nm, greater than or equal to100 nm, greater than or equal to 200 nm, greater than or equal to 500nm, or greater than or equal to 750 nm. Each nanofiber layer in thefilter media may independently comprise synthetic fibers having anaverage diameter of less than or equal to 1 micron, less than or equalto 750 nm, less than or equal to 500 nm, less than or equal to 200 nm,less than or equal to 100 nm, less than or equal to 75 nm, or less thanor equal to 50 nm. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 20 nm and less than or equal to1 micron). Other ranges are also possible.

When present, a nanofiber layer may comprise synthetic fibers having avariety of suitable average lengths. The fibers may comprise staplefibers and/or continuous fibers. Each nanofiber layer in the filtermedia may independently comprise synthetic fibers having an averagelength of greater than or equal to 0.2 mm, greater than or equal to 0.5mm, greater than or equal to 1 mm, greater than or equal to 2 mm,greater than or equal to 5 mm, greater than or equal to 10 mm, greaterthan or equal to 15 mm, greater than or equal to 20 mm, greater than orequal to 25 mm, greater than or equal to 30 mm, greater than or equal to40 mm, greater than or equal to 50 mm, greater than or equal to 75 mm,greater than or equal to 100 mm, greater than or equal to 150 mm,greater than or equal to 200 mm, greater than or equal to 250 mm,greater than or equal to 300 mm, greater than or equal to 350 mm,greater than or equal to 400 mm, greater than or equal to 450 mm,greater than or equal to 500 mm, greater than or equal to 750 mm,greater than or equal to 1 m, greater than or equal to 2 m, greater thanor equal to 5 m, greater than or equal to 10 m, greater than or equal to20 m, greater than or equal to 50 m, or greater than or equal to 100 m.Each nanofiber layer in the filter media may independently comprisesynthetic fibers having an average length of less than or equal to 200m, less than or equal to 100 m, less than or equal to 50 m, less than orequal to 20 m, less than or equal to 10 m, less than or equal to 5 m,less than or equal to 2 m, less than or equal to 1 m, less than or equalto 750 mm, less than or equal to 500 mm, less than or equal to 450 mm,less than or equal to 400 mm, less than or equal to 350 mm, less than orequal to 300 mm, less than or equal to 250 mm, less than or equal to 200mm, less than or equal to 150 mm, less than or equal to 100 mm, lessthan or equal to 75 mm, less than or equal to 50 mm, less than or equalto 40 mm, less than or equal to 30 mm, less than or equal to 25 mm, lessthan or equal to 20 mm, less than or equal to 15 mm, less than or equalto 10 mm, less than or equal to 5 mm, less than or equal to 2 mm, lessthan or equal to 1 mm, or less than or equal to 0.5 mm. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 0.2 mm and less than or equal to 100 m, greater than or equalto 0.2 mm and less than or equal to 500 mm, greater than or equal to 20mm and less than or equal to 500 mm, or greater than or equal to 100 mmand less than or equal to 350 mm). Other ranges are also possible.

When present, a nanofiber layer may have a variety of suitable basisweights. The basis weights of nanofiber layers in which undulations haveyet to be formed, tend to be lower than those that comprise one or moresets of undulations. Forming undulations in a nanofiber layers tends toincrease the amount of the nanofiber layers per area of filter mediafootprint, and thus tends to increase the basis weight of the nanofiberlayers. As described above, fabrication of a filter media may compriseforming undulations in an initially un-undulated nanofiber layers thatthen undergoes one or more processes to form one or more sets ofundulations. For this reason, it may be more facile to refer to thebasis weights of nanofiber layers prior to undulation. These basisweights are equivalent to the basis weights of the nanofiber layers ifextended to remove all undulations therein.

Each nanofiber layer in the filter media may independently have a basisweight prior to undulation of greater than or equal to 0.02 g/m²,greater than or equal to 0.03 g/m², greater than or equal to 0.04 g/m²,greater than or equal to 0.05 g/m², greater than or equal to 0.075 g/m²,greater than or equal to 0.1 g/m², greater than or equal to 0.2 g/m²,greater than or equal to 0.5 g/m², greater than or equal to 1 g/m²,greater than or equal to 1.5 g/m², greater than or equal to 2 g/m²,greater than or equal to 3 g/m², or greater than or equal to 4 g/m².Each nanofiber layer in the filter media may independently have a basisweight prior to undulation of less than or equal to 5 g/m², less than orequal to 4 g/m², less than or equal to 3 g/m², less than or equal to 2g/m², less than or equal to 1.5 g/m², less than or equal to 1 g/m², lessthan or equal to 0.5 g/m², less than or equal to 0.2 g/m², less than orequal to 0.1 g/m², less than or equal to 0.075 g/m², less than or equalto 0.05 g/m², less than or equal to 0.04 g/m², or less than or equal to0.03 g/m². Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.02 g/m² and less than or equal to 5g/m², greater than or equal to 0.05 g/m² and less than or equal to 3g/m², or greater than or equal to 0.1 g/m² and less than or equal to 2g/m²). Other ranges are also possible.

In some embodiments, a nanofiber layer is provided with a carrier layer.The nanofiber may be directly adjacent to the carrier layer, or one ormore layers may be positioned between the carrier layer and thenanofiber layer. In some embodiments, a filter media comprises ananofiber layer and a carrier layer with adhesive positionedtherebetween. The nanofiber layer may have been deposited onto thecarrier layer during formation (e.g., during an electrospinningprocess). In some embodiments, the carrier layer supports the nanofiberlayer and/or allows the nanofiber layer to be handled in a facile mannerwithout undergoing damage.

Some carrier layers are fibrous. For instance, a carrier layer may be anon-woven fiber web, such as a meltblown fiber web and/or a carded fiberweb. In some embodiments, a carrier layer comprises synthetic fibers,non-limiting examples of which include polypropylene fibers, polyesterfibers, and nylon fibers.

When present, a carrier layer may comprise synthetic fibers having avariety of suitable average diameters. Each carrier layer in the filtermedia may independently comprise synthetic fibers having an averagediameter of greater than or equal to 0.5 microns, greater than or equalto 0.75 microns, greater than or equal to 1 micron, greater than orequal to 1.25 microns, greater than or equal to 1.5 microns, greaterthan or equal to 1.75 microns, greater than or equal to 2 microns,greater than or equal to 2.25 microns, greater than or equal to 2.5microns, greater than or equal to 2.75 microns, greater than or equal to3 microns, greater than or equal to 4 microns, greater than or equal to5 microns, greater than or equal to 7.5 microns, greater than or equalto 10 microns, greater than or equal to 12.5 microns, or greater than orequal to 15 microns. Each carrier layer in the filter media mayindependently comprise synthetic fibers having an average diameter ofless than or equal to 20 microns, less than or equal to 15 microns, lessthan or equal to 12.5 microns, less than or equal to 10 microns, lessthan or equal to 7.5 microns, less than or equal to 5 microns, less thanor equal to 4 microns, less than or equal to 3 microns, less than orequal to 2.75 microns, less than or equal to 2.5 microns, less than orequal to 2.25 microns, less than or equal to 2 microns, less than orequal to 1.75 microns, less than or equal to 1.5 microns, less than orequal to 1.25 microns, less than or equal to 1 micron, or less than orequal to 0.75 microns. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 0.5 microns and less thanor equal to 20 microns, or greater than or equal to 1 micron and lessthan or equal to 3 microns). Other ranges are also possible.

When present, a carrier layer may have a variety of suitable basisweights. The basis weights of carrier layers in which undulations haveyet to be formed, tend to be lower than those that comprise one or moresets of undulations. Forming undulations in a carrier layer tends toincrease the amount of the scrim per area of filter media footprint, andthus tends to increase the basis weight of the carrier layer. Asdescribed above, fabrication of a filter media may comprise formingundulations in an initially un-undulated carrier layer that thenundergoes one or more processes to form one or more sets of undulations.For this reason, it may be more facile to refer to the basis weights ofcarrier layers prior to undulation. These basis weights are equivalentto the basis weights of the carrier layers if extended to remove allundulations therein.

Each carrier layer in the filter media may independently have a basisweight prior to undulation of greater than or equal to 5 g/m², greaterthan or equal to 7.5 g/m², greater than or equal to 10 g/m², greaterthan or equal to 12.5 g/m², greater than or equal to 15 g/m², greaterthan or equal to 17.5 g/m², greater than or equal to 20 g/m², greaterthan or equal to 22.5 g/m², greater than or equal to 25 g/m², or greaterthan or equal to 27.5 g/m². Each carrier layer in the filter media mayindependently have a basis weight prior to undulation of less than orequal to 30 g/m², less than or equal to 27.5 g/m², less than or equal to25 g/m², less than or equal to 22.5 g/m², less than or equal to 20 g/m²,less than or equal to 17.5 g/m², less than or equal to 15 g/m², lessthan or equal to 12.5 g/m², less than or equal to 10 g/m², or less thanor equal to 7.5 g/m². Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 5 g/m² and less than orequal to 30 g/m²). Other ranges are also possible. The basis weight of acarrier layer may be determined by weighing a carrier layer of knownarea and then dividing the measured weight by the known area.

As described above, some filter media, such as waved filter media,comprise one or more support layers. The support layer(s) may supportone or more other layer(s) of the filter media that are waved. In anexemplary embodiment, a filter media includes a downstream support layerdisposed on the air outflow side of the waved layer(s) and that iseffective to hold the waved layer(s) in the waved configuration. Thefilter media can also include an upstream support layer that is disposedon the air entering side of the waved layer(s) opposite to thedownstream support layer. The upstream support layer can likewise helpmaintain the waved layer(s) in a waved configuration. As indicatedabove, a person skilled in the art will appreciate that the filter mediacan include any number of layers, and it need not include two supportlayers, or a top layer. In certain exemplary embodiments, the filtermedia can include a single support layer positioned either upstream ordownstream of the other waved layers. In other embodiments, the filtermedia can include any number of additional layers arranged in variousconfigurations. The particular number and type of layers will depend onthe intended use of the filter media.

The support layers described herein can be formed using varioustechniques known in the art, including meltblowing, air laid techniques,carding, spunbonding, and extrusion. In an exemplary embodiment, afilter media comprises one or more support layers that is a carded orair laid web. In some embodiments, a filter media comprises one or moresupport layers that is an extruded mesh.

Various materials can also be used to form the fibers of any supportlayers included in the filter media described herein, includingsynthetic and non-synthetic materials. The support layer or layers maycomprise meltblown fibers, staple fibers, and/or spunbond fibers. In oneexemplary embodiment, one or more support layers are formed from staplefibers, and in particular from a combination of binder fibers andnon-binder fibers. One suitable fiber composition is a blend of at least20% binder fiber and a balance of non-binder fiber. A variety of typesof binder and non-binder fibers can be used to form the media of thepresent invention. The binder fibers can be formed from any materialthat is effective to facilitate thermal bonding between the layers, andwill thus have an activation temperature that is lower than the meltingtemperature of the non-binder fibers. The binder fibers can bemonocomponent fibers or any one of a number of bicomponent binderfibers. In one embodiment, the binder fibers can be bicomponent fibers,and each component can have a different melting temperature. Forexample, the binder fibers can include a core and a sheath where theactivation temperature of the sheath is lower than the meltingtemperature of the core. This allows the sheath to melt prior to thecore, such that the sheath binds to other fibers in the layer, while thecore maintains its structural integrity. This may be particularlyadvantageous in that it creates a more cohesive layer for trappingfiltrate. The core/sheath binder fibers can be concentric ornon-concentric, and exemplary core/sheath binder fibers can include thefollowing: a polyester core/copolyester sheath, a polyestercore/polyethylene sheath, a polyester core/polypropylene sheath, apolypropylene core/polyethylene sheath, a polyamide core/polyethylenesheath, and combinations thereof. Other exemplary bicomponent binderfibers can include split fiber fibers, side-by-side fibers, and/or“island in the sea” fibers.

The non-binder fibers, if present in one or more support layers, can besynthetic and/or non-synthetic, and in an exemplary embodiment thenon-binder fibers can be 100% synthetic. Synthetic fibers may haveadvantageous properties with respect to resistance to moisture, heat,long-term aging, and/or microbiological degradation. Exemplary syntheticnon-binder fibers can include polyesters, acrylics, polyolefins, nylons,rayons, and combinations thereof.

When present, a support layer may include a suitable percentage ofsynthetic fibers. For example, in some embodiments, the weightpercentage of synthetic fibers in each support layer is independentlybetween 80 wt % and 100 wt % of all fibers in the support layer. In someembodiments, the weight percentage of synthetic fibers in each supportlayer is independently greater than or equal to 80 wt %, greater than orequal to 90 wt %, or greater than or equal to 95 wt %. In someembodiments, the weight percentage of the synthetic fibers in eachsupport layer is independently less than or equal to 100 wt %, less thanor equal to 95 wt %, less than or equal to 90 wt %, or less than orequal to 85 wt %. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 80 wt % and less than or equalto 100 wt %). Other ranges are also possible. In some embodiments, oneor more support layers includes 100 wt % of synthetic fibers. In someembodiments, one or more support layers includes the above-noted rangesof synthetic fibers with respect to the total weight of the supportlayer (e.g., including any resins).

When present, a support layer can be formed from a variety of fiberstypes and sizes. In an exemplary embodiment where a filter mediacomprises a downstream support layer, the downstream support layer isformed from fibers having an average diameter that is greater than orequal to an average diameter of the other layers present in the filtermedia. In some cases in which a filter media comprises both an upstreamsupport layer and a downstream support layer, the upstream support layerformed from fibers having an average diameter that is less than or equalto an average diameter of the downstream support layer, but that isgreater than an average diameter of the other layers present in thefilter media. In certain exemplary embodiments, a filter media comprisesa downstream support layer and/or the upstream support layer formed fromfibers having an average diameter in the range of 10 microns to 32microns, or 12 microns to 32 microns. For example, the average diameterof the downstream support layer and/or the upstream support layer may bein the range of 18 microns to 22 microns. In some cases, the downstreamand/or the upstream support layer may comprise relatively fine fibers.For example, in some embodiments, the finer downstream and/or finerupstream support layer can be formed from fibers having an averagediameter in the range of 9 microns to 18 microns. For example, the finerdownstream and/or finer upstream support layer average diameter may bein the range of 12 microns to 15 microns.

When present, a support layer may comprise fibers having a variety ofsuitable average lengths. The fibers may comprise staple fibers and/orcontinuous fibers. Each support layer in the filter media mayindependently comprise fibers having an average length of greater thanor equal to 20 mm, greater than or equal to 50 mm, greater than or equalto 75 mm, greater than or equal to 100 mm, greater than or equal to 200mm, greater than or equal to 250 mm, greater than or equal to 300 mm,greater than or equal to 400 mm, greater than or equal to 500 mm,greater than or equal to 750 mm, greater than or equal to 1 m, greaterthan or equal to 2 m, greater than or equal to 5 m, greater than orequal to 10 m, greater than or equal to 20 m, greater than or equal to50 m, or greater than or equal to 100 m. Each support layer in thefilter media may independently comprise fibers having an average lengthof less than or equal to 200 m, less than or equal to 100 m, less thanor equal to 50 m, less than or equal to 20 m, less than or equal to 10m, less than or equal to 5 m, less than or equal to 2 m, less than orequal to 1 m, less than or equal to 750 mm, less than or equal to 500mm, less than or equal to 400 mm, less than or equal to 300 mm, lessthan or equal to 250 mm, less than or equal to 200 mm, less than orequal to 100 mm, less than or equal to 75 mm, or less than or equal to50 mm. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 20 m and less than or equal to 200 m,greater than or equal to 20 mm and less than or equal to 100 mm, orgreater than or equal to 20 mm and less than or equal to 75 mm). Otherranges are also possible.

When present, a support layer may have a variety of suitable basisweights. The basis weights of support layers in which undulations haveyet to be formed, tend to be lower than those that comprise one or moresets of undulations. Forming undulations in a support layer tends toincrease the amount of the support layer per area of filter mediafootprint, and thus tends to increase the basis weight of the supportlayer. As described above, fabrication of a filter media may compriseforming undulations in an initially un-undulated support layer that thenundergoes one or more processes to form one or more sets of undulations.For this reason, it may be more facile to refer to the basis weights ofsupport layers prior to undulation. These basis weights are equivalentto the basis weights of the support layers if extended to remove allundulations therein.

Each support layer may independently have a basis weight prior toundulation of greater than or equal to 10 g/m², greater than or equal to20 g/m², greater than or equal to 22 g/m², greater than or equal to 33g/m², greater than or equal to 50 g/m², greater than or equal to 60g/m², greater than or equal to 70 g/m², greater than or equal to 80g/m², or greater than or equal to 90 g/m². Each support layer mayindependently have a basis weight prior to undulation of less than orequal to 99 g/m², less than or equal to 90 g/m², less than or equal to80 g/m², less than or equal to 70 g/m², less than or equal to 60 g/m²,less than or equal to 50 g/m², less than or equal to 33 g/m², less thanor equal to 22 g/m², or less than or equal to 20 g/m². Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 10 g/m² and less than or equal to 99 g/m², or greater than orequal to 33 g/m² and less than or equal to 70 g/m²). Other ranges arealso possible. The basis weight of a support layer may be measured byweighing a support layer of known area and then dividing the measuredweight by the known area.

When present, a support layer may have a variety of suitablethicknesses. Each support layer in the filter media may independentlyhave a thickness of greater than or equal to 3 mil, greater than orequal to 4 mil, greater than or equal to 5 mil, greater than or equal to6 mil, greater than or equal to 8 mil, greater than or equal to 10 mil,greater than or equal to 12 mil, greater than or equal to 15 mil,greater than or equal to 20 mil, greater than or equal to 25 mil,greater than or equal to 30 mil, greater than or equal to 40 mil,greater than or equal to 50 mil, greater than or equal to 60 mil,greater than or equal to 75 mil, greater than or equal to 100 mil,greater than or equal to 125 mil, greater than or equal to 150 mil, orgreater than or equal to 175 mil. Each support layer in the filter mediamay independently have a thickness of less than or equal to 200 mil,less than or equal to 175 mil, less than or equal to 150 mil, less thanor equal to 125 mil, less than or equal to 100 mil, less than or equalto 75 mil, less than or equal to 60 mil, less than or equal to 50 mil,less than or equal to 40 mil, less than or equal to 30 mil, less than orequal to 25 mil, less than or equal to 20 mil, less than or equal to 15mil, less than or equal to 12 mil, less than or equal to 10 mil, lessthan or equal to 8 mil, less than or equal to 6 mil, less than or equalto 5 mil, or less than or equal to 4 mil. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 4 mil and less than or equal to 200 mil, greater than or equal to 4mill and less than or equal to 100 mil, greater than or equal to 8 miland less than or equal to 30 mil, greater than or equal to 15 mil andless than or equal to 60 mil, or greater than or equal to 12 mil andless than or equal to 20 mil). Other ranges are also possible. Thethickness of a support layer may be determined by Edana WSP 120.1Standard (2005) with a pressure foot selected to have a 2 ounce load anda 1 square inch area.

When present, a support layer may have a variety of suitable mean flowpore sizes. Each support layer in the filter media may independentlyhave a mean flow pore size of greater than or equal to 30 microns,greater than or equal to 40 microns, greater than or equal to 50microns, greater than or equal to 75 microns, greater than or equal to100 microns, or greater than or equal to 120 microns. Each support layerin the filter media may independently have a mean flow pore size of lessthan or equal to 150 microns, less than or equal to 120 microns, lessthan or equal to 100 microns, less than or equal to 75 microns, lessthan or equal to 50 microns, or less than or equal to 40 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 30 microns and less than or equal to 150microns, or greater than or equal to 50 microns and less than or equalto 120 microns). Other ranges are also possible. The mean flow pore sizeof a support layer may be determined in accordance with ASTM F316(2011).

In one exemplary embodiment, a filter media comprises a downstreamsupport layer and an upstream support layer, as measured in a planarconfiguration, each of which have a thickness of greater than or equalto 8 mil and less than or equal to 30 mil (e.g., greater than or equalto 12 mil and less than or equal to 20 mil), a basis weight of greaterthan or equal to 10 g/m² and less than or equal to 99 g/m² (e.g.,greater than or equal to 22 g/m² and less than or equal to 99 g/m², orgreater than or equal to 33 g/m² and less than or equal to 70 g/m²), anda mean flow pore size of greater than or equal to 30 microns and lessthan or equal to 150 microns (e.g., greater than or equal to 50 micronsand less than or equal to 120 microns).

As described above, some filter media, such as waved filter media,include one or more outer or cover layers disposed on the air enteringside I and/or the air outflow side O. By way of example, FIG. 9Aillustrates a top layer 18 that is a cover layer disposed on the airentering side I of the filter media 1006. In some embodiments, a filtermedia comprises an outer-most layer that is a wire backing. In someembodiments, a filter media comprises a cover layer that can function asa dust loading layer and/or that can function as an aesthetic layer. Inan exemplary embodiment, the cover layer is a planar layer that is matedto the rest of the filter media after assembly and/or waving. The coverlayer may provide a top surface that is aesthetically pleasing. Thecover layer can be formed from a variety of fiber types and sizes. In anexemplary embodiment, the cover layer is formed from fibers having anaverage fiber diameter other than an average fiber diameter of fibers inan upstream support layer, if one is present. In certain exemplaryembodiments, the cover layer is formed from fibers having an averagefiber diameter of greater than or equal to 5 microns and less than orequal to 20 microns. As a result, the cover layer can function as a dustholding layer without affecting the gamma value of the filter media.

In some embodiments (e.g., the embodiment shown in FIG. 9B), a filtermedia includes a bottom layer disposed on the air outflow side. Thebottom layer can function as strengthening component that providesstructural integrity to the filter media to help maintain the wavedconfiguration if the filter media comprises one or more layers that arewaved. The bottom layer can also function to offer abrasion resistance.This may be particularly desirable in ASHRAE bag applications where theoutermost layer is subject to abrasion during use. The bottom layer canhave a configuration similar to the cover layer, as discussed above. Insome embodiments, a filter media comprises both a bottom layer and acover layer. In an exemplary embodiment, the bottom layer is thecoarsest layer, i.e., it is formed from fibers having an averagediameter that is greater than an average diameter of fibers forming allof the other layers of the filter media. One exemplary bottom layer is aspunbond layer, however various other layers can be used having variousconfigurations.

When present, any outer layer(s), such as a cover layer and/or a bottomlayer, can also be formed using various techniques known in the art,including meltblowing, wet laid techniques, air laid techniques,carding, spunbonding, and extrusion. In an exemplary embodiment, thecover layer is an air laid layer and the bottom layer is a spunbondlayer. In some embodiments, a filter media comprises a cover layer thatis an extruded mesh and/or a net. The resulting layer(s) can also have avariety of thicknesses, air permeabilities, and basis weights dependingupon the requirements of a desired application.

When present, a cover layer and/or a bottom layer can comprise fibers ofa variety of suitable types, including synthetic and non-syntheticmaterials. In one exemplary embodiment, a filter media comprises a coverlayer and/or a bottom layer formed from staple fibers, and in particularfrom a combination of binder fibers and non-binder fibers. One suitablefiber composition is a blend of at least 20% binder fiber and a balanceof non-binder fiber. A variety of types of binder and non-binder fiberscan be used to form the media of the present invention, including thosepreviously discussed above with respect to the support layers.

In one exemplary embodiment, a filter media comprises a cover layerand/or a bottom layer, as measured in a planar configuration, each ofwhich independently has a thickness of greater than or equal to 2 miland less than or equal to 50 mil, an air permeability of greater than orequal to 100 CFM and less than or equal to 1200 CFM, and a basis weightof greater than or equal to 10 g/m² and less than or equal to 50 g/m².The thickness of a cover layer may be determined by Edana WSP 120.1Standard (2005) with a pressure foot selected to have a 2 ounce load anda 1 square inch area. The air permeability of a cover layer may bedetermined in accordance with ASTM Test Standard D737 (1996) under apressure drop of 125 Pa on a sample with a test area of 38 cm². Thebasis weight of a cover layer may be measured by weighing a supportlayer of known area and then dividing the measured weight by the knownarea.

As described above, some filter media described herein comprise anadhesive. The adhesive may be positioned between two layers to adherethem together. When present, the adhesive may be positioned in a varietyof suitable locations in the filter media, such as between an efficiencylayer and a scrim, between an efficiency layer and a nanofiber layer,between a nanofiber layer and a support layer, and/or between any othertwo layers in the filter media. In other words, an adhesive may bepositioned between a first layer and a second layer, between a secondlayer and a third layer, between a third layer and a fourth layer,and/or between any other two layers. In some embodiments, a filter mediacomprises adhesive positioned between two separate pairs of layers(e.g., between a first layer and a second layer, and between a secondlayer and a third layer; between a first layer and a second layer, andbetween a third layer and a fourth layer). Properties of some adhesivesare described in further detail below.

A variety of adhesives may be employed in the filter media describedherein. Non-limiting examples of suitable adhesives include pressuresensitive and/or high tack adhesives (e.g., Carbobond 1995), holt meltadhesives (e.g., Bostik HM4105, Bostik 2751). In some embodiments, afilter media comprises a water-based adhesive. In some embodiments, theadhesive is applied in emulsion form. The solids dispersed in theemulsion may comprise an acrylic copolymer.

When present, an adhesive may have a variety of suitable basis weights.The amount of adhesive between any two layers may be greater than orequal to 0.1 g/m², greater than or equal to 0.15 g/m², greater than orequal to 0.2 g/m², greater than or equal to 0.25 g/m², greater than orequal to 0.3 g/m², greater than or equal to 0.35 g/m², greater than orequal to 0.4 g/m², greater than or equal to 0.45 g/m², greater than orequal to 0.5 g/m², greater than or equal to 0.6 g/m², greater than orequal to 0.8 g/m², greater than or equal to 1 g/m², greater than orequal to 1.25 g/m², greater than or equal to 1.5 g/m², greater than orequal to 1.75 g/m², greater than or equal to 2 g/m², greater than orequal to 2.5 g/m², greater than or equal to 3 g/m², or greater than orequal to 4 g/m². The amount of adhesive between any two layers may beless than or equal to 5 g/m², less than or equal to 4 g/m², less than orequal to 3 g/m², less than or equal to 2.5 g/m², less than or equal to 2g/m², less than or equal to 1.75 g/m², less than or equal to 1.5 g/m²,less than or equal to 1.25 g/m², less than or equal to 1 g/m², less thanor equal to 0.8 g/m², less than or equal to 0.6 g/m², less than or equalto 0.5 g/m², less than or equal to 0.45 g/m², less than or equal to 0.4g/m², less than or equal to 0.35 g/m², less than or equal to 0.3 g/m²,less than or equal to 0.25 g/m², less than or equal to 0.2 g/m², or lessthan or equal to 0.15 g/m². Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0.1 g/m² and less thanor equal to 5 g/m², greater than or equal to 0.3 g/m² and less than orequal to 1 g/m², or greater than or equal to 0.3 g/m² and less than orequal to 0.5 g/m²). Other ranges are also possible.

The basis weights described above may be one or more of the followingbasis weights: (1) the basis weight of an adhesive with respect to thefinal filter media; (2) the basis weight of an adhesive with respect toa filter media that has been extended to remove one set of undulationstherein but not another (e.g., extended to remove undulations formed bya waving process but not undulations formed by a gathering process));and (3) the basis weight of an adhesive which has been extended toremove all undulations therein.

In some embodiments, a filter media comprises a pair of layers betweenwhich no adhesive is positioned. Some filter media lack adhesiveentirely. In some embodiments, other methods are employed, in additionto or instead of those using adhesives, to bond layers of a filter mediatogether. For instance, ultrasonic welding may be employed to bond twoor more layers of a filter media together.

EXAMPLE 1

This Example describe the fabrication and testing of filter mediacomprising an irregular structure present at the surface thereof andextending through the uppermost layer therein.

Each filter media was fabricated by adhering a meltblown efficiencylayer to a stretched mesh scrim, and then allowing the stretched meshscrim to recover. First, the mesh scrim and meltblown efficiency layerwere prepared. The mesh scrim and meltblown efficiency layer were cut tothe desired sizes: the mesh scrim was cut to form a 15 inch by 16 inchrectangle, and the meltblown efficiency layer was cut to form arectangle with a width of 15 inches and a length equal to the stretchedlength of the mesh to which it would be applied. Then, the mesh scrimwas placed on a paper blotter, and an adhesive was applied thereto witha medium nap paint roller. The adhesive was a 50 wt %:50 wt % mixture ofwater and Carbobond 1955 (a 55 wt % solids acrylic copolymer emulsion).After coating with the adhesive, the mesh scrim was hung and allowed toair dry for at least 10 minutes.

After the mesh scrim and meltblown efficiency layer were prepared, theywere assembled together to form a filter media. The mesh scrim wasclamped onto a piece of parchment paper disposed on a wooden board bywooden strips affixed thereto by dowel pins. FIG. 10 shows the woodenboard, wooden strips, and dowel pins. Then, the distal wooden strip wasmoved away from the proximal wooden strip to stretch the filter mediauntil the desired degree of stretch was obtained. At this point, themeltblown efficiency layer was gently pressed onto the adhesive-coatedmesh using a lightweight roller device. FIG. 11 shows a photograph of anexemplary meltblown efficiency layer adhered to an adhesive-coated meshstretched to 300% of its initial length. Finally, the meltblownefficiency layer and mesh scrim were removed together from the parchmentpaper and wooden strips, the mesh scrim was allowed to recover, andexcess portions of the mesh scrim uncovered by the meltblown efficiencylayer were cut away. The mesh scrim was allowed to recover by removingthe dowel pins from the distal wooden strip and manually reducing thetension on the stretched mesh scrim. During this process, the meltblownefficiency layer became gathered.

Two sets of filter media were made, both of which included apolypropylene meltblown efficiency layer including fibers with diametersbetween 1 and 3 microns and a SWM X30014 styrenic block copolymer meshscrim. For the first type of filter media (Type A), the polypropylenemeltblown efficiency layer had a basis weight of 7.7 g/m² and wasuncharged. For the second type of filter media (Type B), thepolypropylene meltblown efficiency layer had a basis weight of 32 g/m²and was hydro charged.

For both types of filter media, increasing the degree of stretch of themesh scrim prior to adhesion of the meltblown efficiency layer theretoincreased the gamma, the average surface height, the thickness, and thebasis weight of the resultant filter media up to a degree of stretch of300%. Stretching the mesh scrim to a degree of stretch of 400% did notresult in further increases in these values. Tables 1 and 2, below, showthe effect of initial mesh scrim stretch on several properties of theresultant filter media for filter media of Types A and B, respectively.

TABLE 1 Properties of filter media of Type A Sample No. 1 2 3 4 5 6 7 8Percent stretch of mesh 0%   50%   100% 150% 200% 250% 300% 400% scrimprior to adhesion of meltblown efficiency layer thereto Meltblown basisweight 7.7 10.2 13.5 15.5 19.3 22.2 25.2 24.3 in filter media (g/m²)Percent increase in N/A 33%    75% 102% 152% 189% 227% 216% meltblownbasis weight in comparison to Sample No. 1 Filter media thickness 0.8862.379 2.843 3.035 4.204 4.255 5.493 4.334 (mm) Percent increase in N/A169%   221% 243% 374% 380% 520% 389% filter media thickness incomparison to Sample No. 1 Filter media pressure 2.6 1.9 1.6 1.4 1.2 1.10.9 1.1 drop (mm) Penetration through 58.2% 51.6%   49.6%   51.7%  48.6%   40.9%   36.1%   30.4% filter media Filter media gamma 9.0 15.119.0 20.5 26.1 35.3 49.2 47.0 Percent increase in N/A 67%   111% 126%189% 290% 444% 420% gamma in comparison to Sample No. 1

TABLE 2 Properties of filter media of Type B Sample No. 9 10 11 12 13 1415 Percent stretch of mesh 0%    50%     100%    150%   200%    250%     300%     scrim prior to adhesion of meltblown efficiency layerthereto Meltblown basis weight 33.5 42.8 54.7 68.6 77.2 90.3 99.4 infilter media (g/m²) Percent increase in N/A 28% 63%    105%   130%    170%     197%     meltblown basis weight in comparison to Sample No. 9Filter media pressure 3.2 2.4 2.1 2.1 1.6 1.2 1.3 drop (mm) Penetrationthrough 0.0167% 0.0123% 0.01% 0.01% 0.008% 0.007% 0.004% filter mediaFilter media gamma 118 163 190 190 256 346 338 Percent increase in N/A38%     61%    61%    117%     193%     187%     gamma in comparison toSample No. 9

FIGS. 12 and 13 show the gamma and thickness, respectively, for filtermedia of Type A as a function of degree of stretch of the mesh scrimprior to adhesion of the meltblown efficiency layer thereto. In FIGS. 12and 13, the x-axis is the degree of stretch, which is equivalent to thedifference between the stretched length of the mesh scrim at which themeltblown efficiency layer was applied and the initial length of themesh scrim divided by the initial length of the mesh scrim and thenmultiplied by 100%. FIGS. 14 and 15 show the average surface height(S_(a)) and basis weight, respectively, as a function of degree ofstretch of the mesh scrim prior to adhesion of the meltblown efficiencylayer thereto for both types of filter media. In FIGS. 14 and 15, thex-axis is the ratio of the stretched length of the mesh scrim at whichthe meltblown efficiency layer was applied to the initial length of themesh scrim. FIG. 16 shows the gamma as a function of average surfaceheight for both types of filter media, indicating that gamma increaseswith average surface height.

For filter media of Type B, increasing the degree of stretch of the meshscrim prior to adhesion of the meltblown efficiency layer thereto alsoincreased the irregularity of the surface of the filter media. FIGS. 17and 18 show comparisons between filter media of Type B and simulationsof pleated filter media. The y-axis of FIG. 17 shows the ratio of peakspacing standard deviation to average peak spacing across each sample,which is determined by following steps (1)-(2) of the proceduredescribed above with respect to ISO 16610-21:2011, performing step (4)on each row, and then using standard statistical techniques to determinethe peak spacing standard deviation. The y-axis of FIG. 18 shows theratio of peak height standard deviation to average peak height acrosseach sample, which is determined by following steps (1)-(2) of theprocedure described above ISO 16610-21:2011, performing step (4) on eachrow, and then using standard statistical techniques to determine theheight standard deviation. The x-axis of FIGS. 17 and 18 shows theposition in the sample of the row at which the relevant ratio wasmeasured. The data from the stretched samples is that measured from thesamples described above. The data from the simulated pleats was dataobtained based on simulations of pleated media comprising 10 mm highmini pleats with a pitch of 2.5 mm; variations in pleat height and pitchtypically seen during manufacturing of pleated media were included inthe simulation.

As shown in FIG. 17, the ratio of peak spacing standard deviation toaverage peak spacing increased with the degree of stretch of the meshscrim prior to adhesion of the meltblown efficiency layer thereto. Asalso shown in FIG. 17, the ratio of peak spacing standard deviation toaverage peak spacing was far greater for each filter media of Type Bthan for the simulated pleated filter media. As shown in FIG. 18, theratio of peak height standard deviation to average peak height decreasedwith the degree of stretch of the mesh scrim prior to adhesion of themeltblown efficiency layer thereto. This is because the average peakheight increased with the degree of stretch of the mesh scrim prior toadhesion of the meltblown efficiency layer thereto to a greater degreethan the peak height standard deviation. However, as shown in FIG. 18,for all cases the ratio of peak height standard deviation to averagepeak height for the filter media described in this Example greatlyexceeded that for a simulated filter media having pleats.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. A filter media, comprising: a non-woven fiberweb, wherein: the non-woven fiber web has a stiffness of less than orequal to 100 mg; and the non-woven fiber web has an average surfaceheight of greater than 0.3 mm. 2-5. (canceled)
 6. A filter media,comprising: a non-woven fiber web, wherein: the non-woven fiber webcomprises a plurality of peaks having an average peak height and a peakheight standard deviation; a ratio of the peak height standard deviationto the average peak height is greater than or equal to 0.05; and thenon-woven fiber web has an average surface height of greater than 0.3mm.
 7. The filter media of claim 6, wherein the ratio of the peak heightstandard deviation to the average peak height is greater than or equalto 0.15 and less than or equal to 0.5. 8-9. (canceled)
 10. A filtermedia, comprising: a non-woven fiber web, wherein: the non-woven fiberweb comprises a plurality of peaks having an average peak spacing and apeak spacing standard deviation; a ratio of the peak spacing standarddeviation to the average peak spacing is greater than or equal to 0.08;and the non-woven fiber web has an average surface height of greaterthan 0.3 mm.
 11. The filter media of claim 10, wherein the ratio of thepeak spacing standard deviation to the average peak spacing is greaterthan or equal to 0.15 and less than or equal to 0.5. 12-14. (canceled)15. The filter media of claim 1, wherein the non-woven fiber web is ameltblown fiber web.
 16. The filter media of claim 1, wherein thenon-woven fiber web is charged.
 17. (canceled)
 18. The filter media ofclaim 1, wherein the filter media further comprises a scrim.
 19. Thefilter media of claim 18, wherein the scrim is a mesh.
 20. The filtermedia of claim 18, wherein the scrim is a spunbond web.
 21. The filtermedia of claim 18, wherein the scrim is capable of undergoing areversible stretch of at least 50% along at least one axis.
 22. Thefilter media of claim 18, wherein the non-woven fiber web is adhered tothe scrim by an adhesive.
 23. The filter media of claim 1, wherein thefilter media further comprises a second non-woven fiber web.
 24. Thefilter media of claim 23, wherein the second non-woven fiber web is anelectrospun fiber web.
 25. The filter media of claim 24, wherein thenon-woven fiber web is a meltblown fiber web, and wherein theelectrospun fiber web and a scrim are positioned on opposite sides ofthe non-woven fiber web.
 26. The filter media of claim 1, wherein thefilter media comprises a support layer.
 27. The filter media of claim26, wherein the support layer holds the non-woven fiber web in a wavedconfiguration and maintains separation of peaks and troughs of adjacentwaves of the non-woven fiber web.
 28. The filter media of claim 1,wherein the filter media has a gamma of greater than or equal to
 15. 29.The filter media of claim 1, wherein the filter media has an airpermeability of greater than or equal to 2 CFM. 30-31. (canceled)
 32. Afilter element comprising the filter media of claim
 1. 33-56. (canceled)